This 1 year prospective study involved nine general practitioners in an urban health centre who routinely record all patient contacts on computer. The study determines by comparison with a manual record how accurately doctors record laboratory investigations on computer and compares the effectiveness of three interventions in improving the completeness of computerized recording of presenting symptoms, problems/diagnoses and laboratory investigations. Recording was analysed for 1 month prior to and for two 1 month periods following each intervention. A control group was used. A total of 7983 patient contacts were analysed. Intervention led to an improvement in the recording of presenting symptoms and problems/diagnoses. Recording of investigations on the computer showed no improvement, remaining at one-third of the total in the treatment room book for both study and control doctors. The effectiveness of the different forms of intervention depended on both the aspect of the consultation considered and the familiarity of individual doctors with the method of data collection. Aspects considered less important required greater intervention to bring about a marked improvement, as did doctors relatively new to the practice. It may not be possible to get all aspects of the consultation recorded with the same degree of accuracy. This has implications for the accuracy of retrospective studies dependent on existing computerized data.