To examine whether variations in the number of whole-time equivalent (wte) practice nurses across family health services authorities (FHSAs) can be explained by population characteristics and the organisation of general practice. Analysis of nine health and 16 social indicators for 98 FHSAs identified three factors underlying health care needs. These factors and seven practice characteristics were analysed by stepwise regression. A formula for allocating health care resources and a logistic growth model were used to estimate the 'expected' number of nurses. Past trends indicate an eventual (wte) practice nurse workforce of 12,500 (95% CI +/- 3500). Although geographical disparities have declined, there was a two-fold variation in nurse numbers across FHSAs. Around 2000 (wte) posts would be required to bring under-provided areas, mostly in northern England and metropolitan districts, up to the highest level of provision. There were more nurses in areas with higher proportions of elderly people but fewer where deprivation, morbidity and mortality levels were above average. The number of general practitioners was the most significant predictor of practice nurse provision (t = 5.0); population needs and practice characteristics explained 24% of the variation. The distribution of practice nurses scarcely corresponded with health care needs at the FHSA level. Despite a lack of evidence that nurses are a cost-effective addition to the primary health care team, their role and numbers will be driven by the extent to which they take on responsibilities performed by doctors. Achieving equity in practice nurse provision probably requires explicit consideration in a formula for allocating primary care funds, backed by audit of the services they provide.