Twenty-five general practitioners were interviewed about the contents of out-patient letters. There was universal agreement on the need for the following information: diagnosis, abnormal physical findings, abnormal routine and non-routine test results, changes in treatment, comments on the patient's physical condition and disposal. The contents of 215 out-patient letters were analysed and the results compared with the GPs' views. There was little difference in the letters from medical and surgical clinics. Both were deficient to a limited extent in the reporting of abnormal test results, the reasons for, and significance of investigations, and in detailing the information given to patients.