For 9 days, 12 volunteers ate each day 8 oz of hamburgers and 6 oz of steak barbecued over charcoal. This was followed by a mean rise in high density lipoprotein (HDL) cholesterol of 25%. In addition there was a reduction in total cholesterol (the fall in total less the HDL fraction, which reflects mainly low density lipoprotein cholesterol was 20%). These changes were not seen when 6 of the subjects later ate the same quantity of meat under the same conditions except that it had been cooked in an electric oven. Benzo(a)pyrene and other polycyclic aromatic hydrocarbons have previously been shown to be produced in meat cooked over charcoal, and it is suggested that the resulting induction of the polycyclic hydrocarbon-dependent type of cytochrome P450 is responsible for inducing enzyme activity involved in lipid metabolism. Despite the beneficial effect that such changes in lipids might have on the risk of coronary heart disease, these findings should not be seen as a guide to long-term changes in cooking practice in view of the possible carcinogenic effects of benzo(a)pyrene produced in this way.