Raw and boiled aqueous extracts of garlic (Allium sativum) were administered daily to normal rats both orally and intraperitoneally for 4 wk. The serum levels of glucose, cholesterol, and triglycerides were measured. When the rats were treated with a low dose (50 mg/kg) of raw aqueous extract of garlic, no significant changes in the serum glucose levels were observed compared with the control group. However, there was a significant reduction in the cholesterol level of rats receiving a low dose of garlic (11-14%). Rats receiving garlic orally and intraperitoneally also showed a significant reduction in triglyceride levels (38%). When the rats were treated with a high dose (500 mg/kg) of raw garlic, glucose, cholesterol, and triglyceride levels were significantly affected. When boiled garlic extracts were administered at high concentrations (500 mg/kg), there was no effect on the level of serum glucose. However, a relatively small but significant decrease in the concentration of cholesterol and triglycerides was observed in the serum of the rats receiving boiled garlic. Raw garlic had a profound effect in reducing the glucose, cholesterol, and triglyceride levels, whereas boiled garlic had little effect in controlling these parameters. Therefore because hyperlipidemia is a major etiopathological factor for atherosclerosis, garlic may play an important role in the prevention of atherosclerosis.