Regulation of individual FFA release from adipose tissue has been studied in control, obese and diabetic subjects in the course of glucose tolerance tests. Adipose tissue biopsies were also obtained from some of the subjects. As in previous studies, fasting FFA levels were higher and the fall in FFA was greater in obese and diabetic subjects than in controls. There was a delay in both the fall and subsequent return of FFA. With the decrease of FFA concentration, the contribution of palmitoleic, oleic, and linoleic acids to total FFA decreased, while that of myristic, palmitic and stearic acids increased. The opposite changes were observed as FFA levels rose. Plotting the concentration of individual FFA against the corresponding total FFA level suggested linear regression of the individual FFA concentration on the total plasma FFA level in all three groups of subjects. The percentage contribution of the slope of each regression line to the sum total of the slopes was found to be very similar to the fatty acid composition of adipose tissue. This indicates that the release of individual FFA from adipose tissue is proportional to the total fatty acid composition of adipose tissue above FFA levels of about 200 μEq./L. or more. The existence of a “basal FFA level” is postulated (less than 200 μEq./L.) and a speculative consideration is presented indicating that the latter may be under the primary influence of factors other than adipose tissue.