The safety and efficacy of combined bezafibrate-simvastatin therapy was evaluated in 49 patients with diet-resistant mixed hyperlipidaemia (type IIb). After a two-month placebo phase, patients were randomized to receive either Bezafibrate Slow Release (SR) 400 mg mane or simvastatin 20 mg nocte followed by three months combination therapy. Total cholesterol, triglycerides and high-density lipoprotein (HDL) cholesterol were measured at monthly intervals. Apolipoproteins (apo) A1 and B, lipoprotein (a) [Lp(a)] and fibrinogen were measured before and after each treatment. Simvastatin was more effective than Bezafibrate SR in reducing total cholesterol (2.0 vs. 1.1 mmol/l, p = 0.003) and lowering LDL cholesterol (1.7 vs. 0.4 mmol/l, p = 0.0001) whereas Bezafibrate SR was more effective in reducing triglycerides (by 41% vs. 17%, p = 0.001) and fibrinogen (by 23% vs. 3%, p = 0.004). Compared with simvastatin monotherapy, combined drug therapy induced further reductions in triglycerides (by 26%, p = 0.0003) and apoB (by 11 mg/dl, p = 0.03) and an increase in apoA1 (by 21 mg/dl, p = 0.0008). Symptomatic and biochemical adverse events did not occur more frequently on combined drug therapy than on monotherapy. The combination of bezafibrate and simvastatin was more effective in controlling mixed hyperlipidaemia than either drug alone and did not provoke more adverse events.