The lipid-lowering effect of activated charcoal was studied during a placebo-controlled double-blind prospective trial in 19, mainly hyperlipidaemic patients. Dosages of 15 and 30 g of activated charcoal per day were prescribed for 12-wk periods. Mean serum cholesterol levels ± SD in patients treated with 15 and 30 g of activated charcoal did not decrease significantly (10.2 ± 2.2 to 9.7 ± 2.7 and 10.5 ± 1.5 to 9.7 ± 1.6, respectively). In both the 15- and the 30-g activated charcoal groups, one patient had a significant decrease in serum cholesterol level. No decrease in serum triglycerides was observed in three hypertriglyceridaemic patients. We conclude that activated charcoal in a dosage of 15 or 30 g per day is ineffective in lowering serum cholesterol and triglyceride levels in patients with hyperlipidaemia.