The costs and potential savings associated with switching patients in a hypertension clinic from enalapril maleate to lisinopril were analyzed. Patients taking enalapril were randomized to receive lisinopril or to continue taking enalapril. For the 47 patients randomized, data were collected for 25 patients switched to an equal milligram dosage of lisinopril and for 21 patients who continued to receive a constant dosage of enalapril. To maintain blood pressure control, it was necessary to double the dosage of lisinopril in five patients (20%) and have it in one patient (4%), while the enalapril dosage was doubled in two patients (9.5%). The total direct cost of switching patients to lisinopril was $66.33 per patient. The annual drug cost savings per patient for switching to lisinopril would be $52.08, $46.80, and $120.24 for therapy with one 5-, 10-, and 20-mg tablet per day, respectively. A patient would have to receive 15, 17, or 7 months of therapy with 5-, 10-, or 20-mg tablets of lisinopril, respectively, before a net cost savings would be realized. In the evaluation of a less expensive therapeutic alternative, the total cost of switching must be considered.