The effects on costs and lipid levels of replacing lovastatin therapy with pravastatin were studied. Beginning in April 1992, outpatients receiving lovastatin were switched to pravastatin. Physicians were asked but not required to initiate the pravastatin sodium treatment at half the daily lovastatin dose in milligrams. In October 1993, the dosages of lovastatin and pravastatin and the corresponding lipid-profile results were recorded for each patient for whom lovastatin had been replaced by pravastatin. The drug acquisition cost per year of therapy was calculated for each patient's most recent dosage of lovastatin and pravastatin as of April 1993. The costs used in the analysis were the most recent available (March 1995). Lovastatin therapy was changed to pravastatin in a total of 168 patients. Of the 168 patients, 145 (86%) were prescribed an initial daily pravastatin sodium dose that was at least 50% lower in milligrams than that of lovastatin. All of the 168 patients who received pravastatin had two usable total-cholesterol measurements during lovastatin therapy, and 148 (88%) had at least one such measurement during pravastatin therapy. Among patients with usable serum-lipid data, there was no significant difference between any of the mean serum lipid concentration (total cholesterol, low-density-lipoprotein cholesterol, or high-density-lipoprotein cholesterol) before and after the conversion. The annual cost of lovastatin for the 148 patients would be $71,693 for the most recent dosages; the corresponding cost for pravastatin would be $56,875 (21% lower). The replacement of lovastatin with pravastatin sodium was associated with a 21% cost reduction but no significant change in mean serum lipid concentrations.