This article discusses a quasi-experimental study of the quality of pharmacists' and physicians' drug prescribing for ambulatory hypertensive patients in a health maintenance organization. The null hypothesis was that there is no difference between pharmacists and physicians as to the quality of drug prescribing for hypertensive patients. Analysis revealed no difference in prescribing between the physician group and the pharmacist group on the scoring for the presence of drug interactions, appropriateness of quantities, dose, and patient directions. The pharmacist prescriber group did significantly better than the physician group, however, on choosing the appropriate drug, prescribing for a "positive effect on the patient's health," and overall appropriateness from combining all the above scales (p less than 0.05). The diastolic pressures of the patients assigned to the pharmacists' group were not significantly different from the physicians' group on pretest, but on posttest the diastolic pressures were slightly lower in the pharmacists' group (p less than 0.10).