1. The nonesterified fatty acids (FFA) response in healthy and in coronary subjects were measured after smoking, after insulin and after smoking preceded by glucose or insulin.2. The FFA rose in both groups but more so in the healthy than in the coronary subjects.3. These differences may be due to the fact that the two groups were not sex, and preceding diet.4. As little as 5 gm. glucose intravenously or 0.1 u. insulin for each 10 kg. body weight blocks the FFA rise provoked by smoking.5. The data suggest that the rise in nonesterified fatty acids (FFA) provoked by smoking is a physiologic response to the need for more fuel.