Drug therapy assessments made for ambulatory patients by pharmacists and those made by the patients' primary physicians were compared. Using refill assessment guidelines, pharmacists evaluated the drug therapy regimens of patients attending a general medicine clinic before they were seen by their physicians. At the end of each clinic day, the pharmacists compared their assessments with the physician evaluations. Of the 155 drug regimens reviewed, the study pharmacists would have continued 104 (67.1%) without alteration, changed 48 (31.0%), and referred three patients (1.9%) with new problems for physician evaluation. The differences between pharmacist assessment and physician agreement were not significant (p greater than 0.2), but there was a significant difference between pharmacist assessment and physician actions (p less than 0.005), because the physicians actually changed only 52% of the drugs they agreed could be changed. The study suggests that the pharmacist is able to detect drug therapy problems and to recommend appropriate actions for resolving them.