The principal aim of this study was to examine whether alterations in sweat composition occurred during training. Ten Thoroughbred horses were trained 6 days per week for 9 weeks on a treadmill (+10% slope), 5 at moderate intensity, (80–100% V̇O2max) and 5 at low intensity, (40–45 % V̇O2max). On Day 1 of training and at the end of weeks 1, 2, 5 and 9, the horses performed a standardised exercise test (SET). Sweat was collected onto an absorbent pad lined with plastic and held against the skin with rubber straps. Samples were obtained from the neck and girth areas during exercise and for 10 minutes post exercise. Sweat composition during exercise (in mmol/l) was [Na+] = 143.5, [Cl−] = 181.5, [K+] = 37.5, [Ca++] = 5.1, [Mg++] = 4.2, [urea] = 5.1 and [protein] = 6.4 g/l. Training resulted in a decrease in [Ca++] of 1.6 ± 0.8 mmol/l (P < 0.05) after the first week of training. The type of training had no effect on sweat composition. Sweat produced in the post exercise period had higher [Na+], [Cl−] and [urea] than that produced during exercise. Training does not substantially alter the composition of equine sweat in response to an intense SET.