Early trials of garlic preparations on blood lipids mainly supported a lipid-lowering effect, whereas later well-designed garlic tablet trials were mainly entirely null. However, enteric simulation tests suggest that this discordance may result from ineffective delivery of bioactive agents from the brands of garlic powder (GP) and cyclodextrin-bound garlic oil (GO) tablets tested in some recent negative trials. In contrast, enteric simulation tests show that the preformed bioactive agents present in "traditional" gelatin capsules of GO are efficiently released, although such capsules have rarely been investigated in lipid-lowering trials. It was hypothesized that gelatin capsules of GO given to normal subjects would improve specified coronary heart disease risk factors. Effects of a GP preparation were also investigated. Subjects (n = 51; men and women, mean age 27 y) were randomly assigned to receive either 8.2 mg/d of GO (allyl sulfides) or placebo for 11 wk. Another 27 subjects received garlic powder (GP) of similar biopotential (7.8 mg allicin/d). Outcome measures were 95% confidence intervals (CI) between GO and placebo groups for differences between baseline and subsequent sample times. Men and women combined showed no significant differences save for an improved total antioxidant capacity at 6 wk (P = 0.01). Hence, no benefit from GO after 11 wk is one plausible conclusion. However, there were significant differences in effect of GO between men and women for HDL cholesterol (HDL-C) (P = 0.004) and total cholesterol (TC)/HDL-C (P = 0.003). Women showed favorable effects in terms of CHD risk factors (i.e., increases in HDL-C and reductions in TC/HDL-C), whereas men had small adverse effects. There was a significant difference in the GO effect for glucose (P = 0.006), with a reduction seen for men and an increase for women. The gender effects were unexpected and such analyses were not planned in advance. Confirmation of these findings with larger numbers of subjects would have importance for the use of garlic against CHD and for the design of future garlic studies.