The aim of the present study was to evaluate the capacity of the horse, during low intensity exercise, to increase the contribution of fat oxidation to energy production as a result of a pre-exercise elevation of triglyceride derived plasma FFA. Seven Thoroughbred horses were exercised for 91 min (3.2 m/s for 60 min, 13.4 ± 2.9% V̇O2max) during 2 randomised experimental sessions (test, T and control, C). Prior to the test session, plasma FFA were elevated using a combination of a heparinoid type substance (pentosan polysulphate, 1.3 mg/kg bwt) and a triglyceride emulsion (Iverlip 20; 0.4 g/kg bwt). Mean pre-exercise plasma FFA and triglyceride concentrations were 903.9 ± 275.0 and 810.2 ± 169.6 μmol/l for the test session and 465.5 ± 266.0 and 158.4 ± 64.5 μmol/l for the control session, respectively. Total lipase activity was significantly increased at rest after pentosan polysulphate and Iverlip administration and throughout exercise during the test session. Respiratory exchange ratio (RER) was lower in 5 out of 7 horses and plasma glucose concentration was higher in 4 of these 5 horses during the test exercise session. These results suggest that an elevation of plasma FFA concentration prior to exercise results in an increase in the utilisation of fat, during subsequent low intensity exercise, in a proportion of horses. This effect, however, is probably influenced by individual biological and metabolic variation in the response to exercise and may depend upon the individual's inherent ability to utilise fat.