The welcome appointment of a senior, career health service manager as the National Institute for Clinical Excellence's first chief executive means that work on building up the organisation can now at last begin (see news, page 5). And not before time.

Health secretary Frank Dobson chose to make the pre-Easter launch of NICE rather than the creation of primary care groups the focus of his New NHS reforms, and has greatly raised expectations about the impact it will have on the health service. There is good reason for this: as Mr Dobson and his colleagues have repeatedly argued, quality is more important than structure. But with few of the planned 30 staff yet in post, little office infrastructure, and, rather more importantly, no track record or collective experience to fall back on, NICE will have its work cut out to produce its first clinical guidelines by this autumn.

There is understandable concern that NICE should be seen to have an effect on the NHS - and soon. And with the goodwill of managers, politicians and the professions to buttress its£10m annual budget, it really ought to be able to boast some significant achievements at the end of, say, its first five years.

But if it is to make good progress, NICE will have to establish its credibility. This is something which can be achieved only by producing solid and reliable work which both challenges existing practice and can command professional confidence and widespread support - a seemingly near-impossible task. It should resist the temptation to rush into judgement on issues which simply do not matter, or in such a way that its pronouncements can be discredited. And if that means ignoring the autumn deadline or scaling back the over-ambitious target of 30 to 50 appraisals a year, so be it.