The concentration and profile of the plasma free fatty acid (FFA) pool was determined in three male and three female domestic fowl before and after a 70 min treadmill run. The fatty acid profile of total food lipids was also determined. At rest, palmitic, stearic oleic, and linoleic acids were the main individual fatty acids in the plasma FFA pool and together constituted 50 to 60% of the total. Shorter chain fatty acids (C10 to C15) made up 24 to 38% of the total. In food lipids C16 and C18 fatty acids constituted more than 95% of total fatty acids, therefore food was not a significant direct source of short chain (less than C16) fatty acids. After exercise, there was an 8 to 10 fold increase in plasma FFA concentration. The proportion of lower chain (less than C16) FFA decreased and the proportion of C16 and C18 FFA, in particular oleic acid, increased. At the end of exercise the profile of the plasma FFA pool was similar to that of the adipose tissue triglyceride. Release of fatty acids from adipose tissue may be a major influence on exercise-induced changes in the plasma FFA profile.