Free fatty acid turnover rate was measured by constant infusion of 1‐¹⁴C palmitic acid complexed to human albumin in eight extremely obese patients and in seven controls after a 12‐hour fast. In some of these patients these measurements were performed also during work, in a few of the obese patients before and after physical training. The results were expressed in relation to different body compartments. It was found that free fatty acid turnover rate was higher at rest in the obese than in controls. This difference disappeared when free fatty acid turnover rate was calculated per kg body weight or per kg body fat. When calculated per kg lean body mass, however, the obese patients again had higher values of free fatty acid turnover rate than the controls. During a standard work load the obese did not show lower free fatty acid turnover rates during work than the controls, even if the increase in two of the obese patients, who had a high turnover rate at rest, was small during work. The results thus give no evidence of a decreased fatty acid turnover rate in obesity. On the contrary, after fasting for 12 hours it seems to be higher than normal.