Tom Sackville, the junior health minister, confirmed he has held talks with Salick Healthcare, a specialist Californian health provider.
The US company has already held discussions with the Royal Marsden cancer hospital in London and is to meet officials from the Christie, Manchester, a specialist cancer centre, this week.
Mr Sackville - who is heading the Government's drive to get more private involvement in the NHS - said he had met representatives from Salick in June.
'They specialise in diagnostic and therapeutic services for patients suffering from cancer and kidney failure,' said Mr Sackille.
'They also serve patients who have had organ transplants, and those suffering from immuno-deficiency diseases.' They were, he said, 'one of a number of American companies trying to gain a foothold in the UK'.
Mr Sackville added: 'I explained that while we are encouraging the NHS to co-operate with the independent sector, we as a department, remained strictly neutral in the negotiating process.
'It is for NHS trusts or GP fundholders to negotiate their own partnership deals and to satisfy themselves on the financial viability and clinical efficacy of services offered.'
But Labour accuses the Government of seeking to sell off 'lucrative segments of the NHS to the Americans'.
Dawn Primarolo, the party's shadow health minister, said: 'The American system is the most expensive and just about the most inefficient in the world'. She added that the introduction of American health-care companies should be resisted 'at all costs'. The Royal Marsden Hospital, whose London site had been threatened with closure, refused to comment.
The Christie Hospital said Salick had asked for a meeting, although it did not yet know precisely what the company was proposing. Any suggestion that the Christie would be sold to an American health care company was 'daft' a spokesman said.
Renewed United States interest in the NHS market comes as health companies fear a squeeze from Bill Clinton's health care reforms.
Previous large-scale involvement in the British private hospital market by US firms has tended to end in retreat, and the private sector in Britain has also been disappointed at how little business has come its way since the NHS changes were implemented in 1991.
David Blunkett, Labour's health spokesman, said: 'We must have become a soft touch for easy profits.'