The ingestion of garlic has been reported to have many cardiovascular effects, including a reduction in plasma cholesterol concentration and the susceptibility of LDL to oxidation. A double-blind, placebo-controlled, randomised crossover study was conducted in subjects with mild to moderate hypercholesterolaemia who were subject to strict dietary supervision and assessment. After a baseline dietary period of 28 days, subjects took Kwai garlic powder tablets 300 mg three times daily or matching placebo for 12 weeks, followed by 28 days washout, followed by a 12 weeks crossover on the alternative preparation. In the analysis hypercholesterolaemia was defined as those subjects in the range 5.5-8.05 mmol/l. Three subjects were withdrawn, one allocated to garlic and complaining of garlic body odour, one using placebo having intercurrent health problems, and one with a baseline cholesterol below 5.5 mmol/l, yielding analysable results in 28 subjects. Comparing the period on garlic with that on placebo, there were no significant differences in plasma cholesterol, LDL cholesterol, HDL cholesterol, plasma triglycerides, lipoprotein(a) concentrations, or blood pressure. Mean LDL cholesterol concentration was 4.64 +/- 0.52 mmol/l on garlic and 4.60 +/- 0.59 mmol/l on placebo. There was no demonstrable effect of garlic on oxidisability of LDL, on the ratio of plasma lathosterol/cholesterol (a measure of cholesterol synthesis), nor on LDL receptor expression in lymphocytes. This study found no demonstrable effect of garlic ingestion on lipids and lipoproteins.