The activity of 34 general practitioners (GP) working in solo practices in six Local Health Units were assessed, as a preliminary step of a main study, to evaluate and possibly improve the quality of GP professional performance using peer review and feed-back information. A wide interpractice variation was observed in patient visit and patient visiting rates, drug and test prescribing, in- and out-patient referrals, as well as in the composition of the practice case-mix. The extent of interpractice variation for relevant actions in the process of care was unchanged after adjusting for case-mix, suggesting that case-mix differences have little effect in explaining differences among physicians' overall pattern of care and health care resource consumptions.