The aim of this study was to evaluate how training affects plasma total, free and esterified L-carnitine concentrations in horses. The study was done on a total of 32 healthy, trained purebred Arabian horses. The 32 horses comprised two groups. In the first group, 12 stallions and 6 mares three-year-old horses involved in race-training were studied at rest. In the second group, 14 stallions were studied during a typical race or endurance training session. Jugular venous blood samples were collected to determine lactic acid (LA), free fatty acids, glycerol, triacylglycerides (TG), and the total esterified and free L-carnitine contents. The race training session caused a significant increase in blood LA and plasma esterified L-carnitine, glycerol, and TG levels. It also caused a decrease in the plasma free L-carnitine concentration determined just after the end of exercise. Compared with endurance training, high-intensity racing exercise increased the plasma esterified L-carnitine concentration and decreased that of free L-carnitine according to training intensity.