Relationships between use of pharmacy computers and performance of selected professional activities were investigated, via a survey of southern Michigan pharmacists. Respondents included users of two major computer systems as well as pharmacists who do not use computers. A net response rate of 65.7 percent (213 usable questionnaires) was achieved. In general, computer users reported encountering more drug-related problems than did nonusers and more frequent contacts with prescribers for drug-therapy problems. Little difference was found between the two groups in regard to patient counseling activities, except that computer users were more likely to use auxiliary labels. When responses from users of the two computer systems were examined separately, results suggested that one of the systems contributed positively to certain aspects of pharmacists' professional activities while the other system had little influence. These results indicate that it may not be possible to state general conclusions about the effect of computers on the professional practice of pharmacy.