The economic decisions taken by family doctors in one family practitioner area in the north of England were examined. There was evidence of a differential response to professional and economic incentives by a group of "high investing" practices. On five indicators of improvement in practice 32% of the practices accounted for 71% of the positive scores. Nearly all the high investing practices were in affluent areas; they were on average larger and had younger partners than the other practices. The high investing practices also faced more financial problems. There was evidence that older doctors with long lists of patients had a different strategy of income maximization. Innovation in primary care is not determined by attitude alone but also by objective factors such as age, location, and size of the practice.