The present study concerned several aspects of peer consultation by general practitioners, investigated in a group of 184 doctors (response rate: 83%) who had their vocational training in the department of general practice of the University of Utrecht and practised for at least three years at the time of the study. Questionnaire responses indicated that consultation during and outside surgery hours and participation in case-discussion groups generally extended over more than two years, occurred frequently, and usually pertained to diverse problems associated with diagnosis and treatment. Participation in study and peer review groups extended usually over a shorter time (1 to 1 1/2 years) and the problems dealt with were predominantly the same as for individual consultation. One-third of the general practitioners consulted colleagues frequently and continued to do so for long periods, dealing systematically with a variety of problems; one-third did so infrequently or unsystematically, and one-third did little or not at all. A relationship was found between the setting of the practice and consulting behaviour: 20% of those who practised alone never consulted peers, whereas those in group practices and health centres were accustomed to do so regularly.