Are we seeing the start of a wave of top-name departures from the NHS? Chief executive Sir Alan Langlands will leave for Dundee at the end of the summer, while director of planning Alasdair Liddell is moving to Internet company iMPOWER. Various changes are being mooted in the Scottish service, where rumours surface daily that chief executive Geoff Scaife may not have his contract renewed. (He is still in place, busy dismissing such speculation. ) A rung down, Mike Fry, a rare survivor from the heady days of first-wave trusts, is leaving Manchester's Christie Hospital. And Tim Matthews, chief executive of Guy's and St Thomas' trust, is going to the Highways Agency - ironically, treading a similar path to Derek Smith, who left King's Healthcare trust to run London Underground last year. Mr Matthews himself admits that he feels 'part of an era' that is moving on.

In general, the turnover of chief executives in the NHS is too fast. People are lucky to get two or three years in post: barely enough time to change the stationery, much less the organisation. But those who manage to stay for the long haul are also under relentless pressure. There is political pressure from ministers anxious for rapid results, or local MPs keen to make a noise on behalf of patients. And woe betide any chief executive who generates negative headlines. Dick Bishop, who this week announced his early retirement from Portsmouth Hospitals trust, is not alone in finding himself clearing his desk after the tabloids have been on the phone.

There is the inevitable pressure of running a large organisation. And there is the pressure of doing a different job one year from another. The job Mr Fry was lately doing at Christie Hospital can have borne little resemblence to the one he was doing as it went for trust status.

All this is pushing people in their mid-40s and 50s, who still have 10 or 15 years of working life ahead of them, out of the health service. Some who are forced out tend to end up in consultancy or languishing in a curious limbo - doing part-time work or running a charity. Those who leave voluntarily seem to be going to other high-profile posts, often in public service. But they are no longer looking to the NHS for their next challenge.

It is hard not to wish them well. But it seems a shame that so much experience is being lost and that so many NHS careers are being brought to a premature close.