Objective: The effect of pravastatin was evaluated using patient data accumulated in the data base of a hospital information system (HIS). Methods: We selected 130 patients treated with pravastatin 10 mg per day, for a minimum period of 4 weeks. Results: In the t test analysis, the reduction rates of total cholesterol (TC) and low-density lipoprotein (LDL) levels for pravastatin administration were 18%, and 27%, respectively. These values were similar to previous reports. The high-density lipoprotein (HDL) level, however, did not change significantly, although previous reports have shown an elevation of HDL levels. In an attempt to explain the origin of this difference, we studied the pretreatment value dependence of the cholesterol change using regression analysis. We found that pravastatin raised the HDL level in those cases where pretreatment values were lower than 58 mg.dl(-1) and reduced it for higher values. We also showed that the reductions of TC, LDL and triglyceride (TG) levels correlated positively with their pretreatment values.