Choosing an Internet service provider (ISP) has never been easier if you want a dial-up account for personal use. Look in the back of any Internet magazine in the UK and you will find 160-plus companies touting for business at an average cost of u10 a month.

But if you're in a large organisation which wants to hook its existing networked infrastructure into the Internet, and maybe even contemplate that first move down the much-hyped yellow brick road to the intranet, the focus becomes much narrower.

At least, that's the message peddled by the three biggest players in the US market, which have all gained a presence in the UK in the last year. Player number one, UUNet, established a European beach-head last November with the takeover of Unipalm Pipex.

In February, just down the road from the UUNet Pipex headquarters in Cambridge, arch rival Performance Systems International (PSI-Net) set up shop, having quietly bought up the EUNet UK customer base the previous summer. PSI-Net has chosen to focus on direct sales to large organisations, a low-profile route which makes much of its higher performance backbone in the UK and has won a sizeable corporate following.

The third player, Netcom, opened for business on 1 May in Bracknell.

It chose to build its business organically and establish its name by way of an aggressive national marketing campaign. It now claims a 10,000 dial-up UK user base and is gearing up for a wider assault on the business market.

The presence of all these 'internationally focused' ISPs is putting a lot of pressure on the UK companies, such as BT Internet, Demon Internet and Planet Online, which are all touting for big business customers.

But in recent months, the US ISPs have been marketing much more aggressively against local providers. They argue that big organisations, particularly multinationals, need to think first and foremost about hooking up with an ISP which operates on an international scale.

'The corporates need to make sure the international backbone is there when they choose a supplier. Multi-nationals want lots of bandwidth, they don't want low transmission speeds,' said Martin Temple, UUNet Pipex product and services group manager. The only way you can guarantee that is to own the backbone yourself, and lots of it.'

Because so much international traffic on the Net originates in the US, large companies need to consider the infrastructure of the ISP on the other side of the Atlantic. 'We've invested heavily in building up our infrastructure in the US and we've spent $16m setting up here and establishing our transatlantic links,' said David Furniss, sales and marketing manager at Netcom. 'The quality of our American network is important, especially if a customer is expecting a lot of US hits. We can provide mirrored sites in the US which can deal effectively with a high level of interest.'

Even closer to home, there's European connectivity to consider. PSI-Net has announced a $100m investment in pan-European infrastructure. 'It's all going to be frame relay technology,' said Dorothy Briggs, PSI-Net marketing manager, 'and that advanced system gives us tremendous performance advantages over our rivals.'

Not to be outdone on the future-proof technology front, Netcom has revealed it is talking to Energis, the National Grid's telecoms subsidiary, which is offering its frame relay and ATM infrastructure to ISPs. 'We have to decide whether to invest in duplicating that infrastructure over here,' said Furniss, 'or use what's already there and available now.'

Naturally, the homegrown providers are starting to hit back at the US companies where it hurts most - their pockets. The installation and first-year operating cost for a top-of-the-range 2Mbps leased line connection costs just over #44,000 from UUNet Pipex, while Demon charges customers in the 0171 area nearer #33,000. James Gardiner, Demon marketing manager, said: 'People have to ask themselves, is this the best value for money?

They need to ask about support, cost and quality of service, and we can match all that.'

US-based suppliers are starting to push the message out on other key fronts. They are talking up their Web design and Web hosting services, facilities managed servers and support for networking resellers which already supply and service the business community.

UUNet Pipex offers an in-house Web design service called Online Publishing, which employs 20 staff. The company has put together sites for the Royal Mail, Barclaycard, Legal & General and Thomas Cook. 'These are customers who we've provided with Internet access, who have then asked us to design their sites,' said Temple. 'They want it to be corporate-looking but functional in some way. '

'Initially we weren't going to offer our Pipeline single-user dial-up product in the UK,' said PSI-Net's Briggs. 'But then we started working with the TUC, which wants to link union members into central database services and need individual dial-up accounts. So now we'll offer that, although it will probably be badged with the name of the organisation.'

Another trend, according to Temple, is the movement away from Web servers within large organisations towards leased line links. 'A lot of security and support issues surround in-house servers,' he said. 'We're now offering a facilities managed server, which is a whole dedicated machine that we look after for an organisation. We've got one up and running for British Airways at Telehouse in the Docklands, which is an extremely high-security installation, far more secure than anything a company could devise for itself.'

But most important of all is the aggressive manner in which these ISPs are targeting the network resellers which already have a supply and support relationship with the largest organisations. Big names such as Computacenter, BSG and Stream have linked up with PSI-Net to supply its products to their clients. The Netcom team includes ex-Compaq staff who devised the very successful reseller strategy which took enormous bites out of IBM's market share in the 1980s. 'We need to alert resellers to the opportunities in the forthcoming "Year of the Intranet", as we did with the "Year of the LAN",' said Furniss.

First off the blocks is UUNet Pipex, which has 80 resellers signed up and is touting for more team members. 'Companies are looking for solutions to all their needs, from LAN to WAN and out onto the Internet,' said Temple.

'We are long past the stage when any single aspect of networking can be considered in isolation.'

Once more, it seems, the Yanks are over here, and widening our horizons.