Evaluation by Participants: For a project aimed at improving the prescribing performance of general practitioners (GPs) in Northern Hessia, 53 GPs who exceeded average prescribing costs by more than 20% were approached. 32 agreed to participate in 10 peer-review group meetings and to discuss an analysis of their own prescriptions issued during a three-months period. These 32 GPs in three quality circles as an intervention group were compared with a group of 15 GPs as a "gold standard" who had been working for two years already on other items than rational prescribing and who had not had any problems with prescribing costs. Apart from positive effects in changing actual prescribing behaviour, discussed elsewhere, an evaluation of the group work by participants in structured questionnaires and open discussions revealed differences between the intervention and the "gold standard" groups. Members of the intervention group had to overcome feelings of being controlled by the authorities in the first session, and felt less satisfied with the effect of the group work on their daily work in practice. This article discusses matters of working in groups, and points out the importance of volunteer participation.