Lipid management is well established as an effective preventive and management tool for cardiovascular disease (CVD). Health claims regarding the cholesterol lowering benefits of garlic are widespread. However, the clinical trial data are inconsistent. The effect of two doses of a commercial garlic preparation on plasma lipids were evaluated, compared to a placebo, in moderately hypercholesterolemic adults (baseline low density lipoprotein cholesterol (LDL-C)=157. 4+/-18.7, mean+/-S.D.). Fifty-one adults, aged 51.8+/-8.3 years participated in a double-blind, placebo-controlled, parallel treatment trial conducted in an outpatient research clinic. They were randomized to a placebo or a garlic botanical blend providing 500 or 1000 mg dehydrated garlic powder/day (three groups, 16-18 subjects per group). Plasma lipids were assessed every 2 weeks for 12 weeks. The study was designed with sufficient power to detect a 10% relative decline in LDL-C. The absolute mean changes in LDL-C over 12 weeks were 0.0+/-4.3, +1.4+/-4.8, and -10.1+/-6.8 mg/dl for the placebo, half-dose and full-dose, respectively. In the full-dose group, the LDL-C decrease of 6.1% was not significantly different from the other groups (P=0.5). No significant differences were observed for total- or high-density lipoprotein cholesterol (HDL-C), or triacylglycerol levels. In conclusion, the garlic powder preparation used in this study among moderately hypercholesterolemic adults did not significantly effect plasma lipids levels. There was no indication of a graded affect by garlic dose over the range of 0, 500 and 1000 mg/day. A small (<10%) effect on LDL-C levels or a threshold effect requiring larger doses are not eliminated by this study.