Formal studies of computerized information systems for ambulatory patients are rare. As part of an evaluation of the effects of such a system on clinic function, we divided the residents in our teaching clinic into a study group with access to COSTAR and a control group with access to conventional medical records alone. Nurses and clerical personnel in the clinic were allowed to use the computerized records only for patients of residents in the study group. We sampled the attitudes of nurses and clerical personnel toward use of the computer and performed detailed time studies of patient flow in the clinic. Responses to questionnaires reflected acceptance of computerization by the personnel sampled, who favored COSTAR records over conventional records, primarily because of the increased availability of information for telephone management and demand care. The residents never became facile users of COSTAR--a problem that we attribute to the infrequency of their clinic sessions. As a result, and because the workloads of residents using COSTAR were larger, waiting times were longer in clinics attended by these residents. Overall, the most intensive users of the computerized medical records were not the physicians. Improved productivity and better use of time among the nurses and clerical personnel were thought to outweigh the residents' perceptions.