1. Claims for beneficial effects on cholesterol levels, fibrinolytic activity, and platelet aggregation are attributed both to fresh garlic and onions (or their extracts) and to commercially available preparations. 2. Regarding fresh garlic, the claims have been confirmed, but so far only at very high dosages. 3. For onions and commercially available supplements contradictory results have been reported. 4. All published trials showed severe methodological shortcomings. Some trials were not randomized and/or not blinded whilst this was possible, and in only one of every three studies more than 25 patients participated in each treatment group. In no trial was prognostic comparability of the treatment and the control groups ascertained. At the moment there is inadequate scientific justification for garlic supplementation.