To evaluate whether the amount of experience of sport horses and the stress of transport affected their adrenocortical and thyroid responses, the plasma concentrations of total cortisol and total and free iodothyronine of 63 horses were studied before and after show jumping competitions. There were 14 trained inexperienced jumpers (group 1), 20 trained experienced jumpers (group 2), 10 trained inexperienced jumpers that had been transported just before the competition (group 3) and 19 trained experienced jumpers that had been transported just before the competition (group 4). The concentrations were measured under basal conditions and five and 30 minutes after the competition. There were significant increases relative to the basal values in the total cortisol concentrations of all four groups of horses at five and 30 minutes (P<0·001), but there were no significant differences between the groups. In contrast, there were no significant changes in the concentrations of triiodothyronine, thyroxine and free thyroxine after the competition and there were no significant differences between the groups. However, the horses in group 2 had significantly lower basal concentrations of free triiodothyronine than the horses in groups 1, 3 and 4 and the difference was maintained at five and 30 minutes after the competition.