Combined hyperlipidaemia and the presence of small and dense LDL particles in the circulation are associated with an increased risk of myocardial infarction. The effect of pravastatin on plasma lipoproteins and on LDL size has been evaluated in a single-blind, randomised, placebo-controlled study in 24 patients with combined hyperlipidaemia; 12 patients on pravastatin and 12 on placebo. After 16 weeks on pravastatin, plasma total (-15%) and LDL (-23%) cholesterol and apo B (-13%) levels were significantly reduced and apo AI (+6%) had increased. LDL size (measured by gradient gel electrophoresis) had not changed. No adverse effect was observed. The study suggests that, in combined hyperlipidaemia, LDL size is not affected by variation in LDL receptor activity.