The nature of the work undertaken by different health professionals an
d inter-professional boundaries are constantly shifting. The greater k
nowledge of users of health care, and the increasing technical and org
anizational complexity of modern medicine, have partly eroded the cont
rol of health professionals over the substance of their work. The defi
nition of a field of work as lying within the province of any one prof
ession is culturally rather than scientifically determined. It is evid
ent that care of good quality should be delivered at the lowest possib
le cost. This might include delivery of care by a less trained person
than heretofore, or by someone with limited but focused training. Shar
ing of skills is a more sensible subject for discussion than transfer
of tasks. We review a number of studies which show the effectiveness o
f inter-professional substitution in various care settings, and also t
he effectiveness of substitution by those other than health profession
als, The views of users of health services on inter-professional subst
itution need to be considered. Health professionals and others need to
work together to devise innovative ways of delivering effective healt
h care. The legal issues need clarification.