The effects of the electronic display of guideline-based, patient-specific treatment suggestions on pharmacist work patterns were studied. A total of 28 pharmacists at a hospital-based ambulatory care pharmacy were randomly assigned to intervention and control groups. The intervention group had access to electronic treatment suggestions for heart failure, ischemic heart disease, reactive airways disease, and uncomplicated hypertension, while the control group did not. Starting 9 and 19 months after the initial display of treatment suggestions, all pharmacists recorded the time they spent on a variety of activities, the purpose of each activity, and persons contacted during the activity; these observations were recorded in response to a pager-like device that randomly buzzed four times an hour. A total of 11,102 observations were recorded. Pharmacists in the intervention group spent significantly more of their time discussing information, advising and informing, and solving problems than pharmacists in the control group but significantly less of their time checking and filling prescriptions. Pharmacists in both groups completed a majority of their work alone, but pharmacists in the intervention group worked significantly less by themselves and significantly more with other pharmacy personnel, patients, and physicians and nurses than control-group pharmacists. The delivery of patient-specific information to pharmacists at the time of dispensing had a significant positive impact on pharmacist work patterns.