The effect of the combination of low-dose lovastatin and low-dose colestipol was studied among 57 subjects with moderate to severe primary hypercholesterolaemia (total cholesterol > or = 7.0 mmol l-1). Following an 8-week dietary phase, participants were randomized to treatment with 20 mg of lovastatin combined with 5 g or with 10 g of colestipol, or to matching placebo. Baseline total cholesterol was 7.7 +/- 0.9 mmol l-1 after dietary stabilization. Total cholesterol levels were reduced to 5.6 +/- 0.7 mmol l-1 and 5.8 +/- 0.7 mmol l-1 after 4 and 8 weeks of treatment in the lovastatin 5 g-1 colestipol group, and 74% of the subjects achieved the goal of low density lipoprotein (LDL) cholesterol levels of > or = 4.0 mmol l-1. Among the lovastatin 10 g-1 colestipol group, total cholesterol was reduced to 5.4 +/- 0.5 mmol l-1 and 5.5 +/- 0.9 mmol l-1 following 4 and 8 weeks, and 80% of subjects achieved the LDL cholesterol goal. No change was seen in the placebo group. Thus, low-dose combination therapy with lovastatin and colestipol, in conjunction with dietary treatment, is effective in moderate to severe primary hypercholesterolaemia, and is well tolerated.