The side effect profiles and lipid lowering efficacy of nicotinic acid (1 g three times daily) and its analogue acipimox (250 mg three times daily) in type 2b hyperlipidaemia were compared in a double-blind placebo controlled study. In the nicotinic acid group (n = 7) at 12 weeks there were significant reductions (P less than 0.05) with respect to placebo (n = 9) in total cholesterol (median and range) 6.6 mmol l-1 (4.8-8.4) vs 8.8 mmol l-1 (7.5-9.5), triglyceride 1.4 mmol l-1 (0.5-4.6) vs 2.8 mmol l-1 (1.5-9.5) and apoprotein B 88.6 mg dl-1 (62.1-114) vs 121.9 mg dl-1 (88.0-170.7). In contrast there was no significant alteration in lipids in the acipimox group (n = 12). Nicotinic acid was associated with a high incidence of side effects, principally cutaneous flushing, while acipimox was well tolerated by all patients.