The Institute of Healthcare Management has admitted to having just 8,500 members - up to 1,500 fewer than was claimed when it was formed in October last year.
In an 'interim report' on the IHM's first nine months, to be presented to its annual conference next week, chief executive Stuart Marples also admits that 'influencing the external agenda' was not a 'top priority' for the new organisation.
But he says the IHM was 'disappointed not to be more closely involved in the development of the NHS plan'.
The former Institute of Health Services Management claimed that 8,000 members at the beginning of 1999.
The Association of Managers in General Practice was reported to be about a quarter of that size when it voted in October 1998 to merge and form the IHM .
In his report, Mr Marples blames 'a tidy up of the system for lapsed subscribers' during a database merger for a 'one-off reduction in numbers'.
But deputy chief executive Suzanne Tyler said that only 1,195 AMGP members had transferred, although financial estimates had been made 'working on the basis of 1,500' AMGP members.
She added: 'We had more joint members than we thought we would have, ' but later clarified that only 60 to 70 people had been members of both the AMGP and the IHSM.
The IHM acknowledges in a draft membership recruitment drive on its website that membership is the 'lifeblood of any professional organisation'.
The draft poses a series of questions for consultation around key issues and poses fundamental question such as 'What does [the IHM's name] stand for? and 'What are we offering?'
Ms Tyler said the IHM had acquired 869 new members since October last year and it was 'difficult to tell' whether the new organisation had lost or gained members since the merger.
Mr Marples' report brings some relief to the remaining IHM membership, with unaudited accounts for 1 October 1999 to 30 June 2000 showing an operating surplus of more than£30,000.
This is a vast improvement on the last available audited accounts - for the year to December 1998 - which recorded a£375,000 deficit for the IHSM.
'Finances are stabilised now, with healthy reserves and a small surplus on the year expected, 'Mr Marples reports.
Accounts for the period between December 1998 and the merger in October are not available but should be published in March or April next year.
Health Quality Service director Peter Griffiths, IHSM president in 1995-96, said keeping a professional organisation like the IHSM going 'on relatively small numbers' had always been a difficult job and was 'no easier now'.
He said he hoped the IHM would give serious consideration to working more closely with other organisations, such as the Institute of Management, which he thought now had as many NHS managers as the IHM.
A graph on the IHM's website claims just 42 per cent of its members are junior, middle or senior NHS managers, while 15 per cent work in the primary care sector and the rest are students, retired or employed in the independent sector.
Health management consultant Peter Stansbie, IHSM president 1994-95, said the IHM was now on an 'even keel'.
He added: 'I wouldn't be too worried about membership figures straight away.
'Always, when organisations merge, there are some people who review their membership. '
NHS Retirement Fellowship director Roger Stokoe, president in 1992-93, said: 'I think that trend will be reversed - we can only go forward now.
'I'm confident in that and in Stuart Marples. '