Garlic has long been used for medicinal purposes. It has been shown that different forms of garlic have significant antioxidant effects. The strong flavor, odor and unwanted gastrointestinal side effects of fresh garlic has rendered the use of commercial garlic supplements as a preferable option. To investigate the effects of garlic supplementation on serum total antioxidant capacity and lipid parameters, 17 healthy volunteers were administered four standardized commercial garlic tablets every day for 30 days. Blood samples were taken at day 1 (before the first administration of tablets [control] and at 3 h after the administration of tablets), 15 and 30 days, respectively. Total antioxidant capacity (TAC), total cholesterol, low density lipoprotein cholesterol (LDL cholesterol), high density lipoprotein cholesterol (HDL cholesterol) and triglyceride (TG) were measured in sera. Serum TAC was increased significantly at 30 days compared with 15 days, 3 h and control. There was also a significant increase in serum TAC at 15 days compared with 3 h and control. Total cholesterol, LDL cholesterol, HDL cholesterol and TG were not found to be significantly different between control, 3 h, 15 and 30 days. These data suggest that garlic, used as a dietary supplementation, may be beneficial in increasing the antioxidant capacity of the body. Copyright © 2009 John Wiley & Sons, Ltd.