Serum cortisol and insulin concentrations were determined in 30 patients with primary hyperlipoproteinemia (HLP) phenotype IIa (20 persons) and IIb (10 persons) during treatment with lovastatin. Lovastatin dosage varied from 20-80 mg daily. Serum insulin concentration did not change significantly after lovastatin treatment. Serum cortisol concentration significantly increased after 12 weeks of treatment. Cortisol concentration changes were different in HLP IIa and IIb patients. In HLP IIa cortisol concentration increased from 21.9 micrograms/dl to 28.1 micrograms/dl after 12 weeks of treatment, in HLP IIb cortisol level decreased from 31.3 to 24.1 micrograms/dl after 4 weeks of treatment and increased to 32.3 micrograms/dl after 12 weeks of therapy. Mean cortisol concentration was significantly higher in HLP IIa than HLP IIb patients. LDL-cholesterol concentrations changes after treatment correlated significantly with baseline cortisol concentration in HLP IIa group (r = -.34), changes in HDL-cholesterol concentration with baseline insulin levels in HLP IIb patients (r = -.54).