The study was conducted in Biały Bór and Bogusławice Training Centres in the years 2003-2005. The study was carried out in two stages (I stage – first week of training period; II stage – at the end of training period). The study included 253 half-bred stallions that were given into excitabilitytest by Budzyński's method. Simultanously the heart rate, respiratory rate and body temperature (at rest and in test) were measured. A statistically significant influence of studied stallions' breed on the level of measured clinical indices was found. The training process in the Training Centre influenced favourably the heart rate value measured to stallions in particular stages of the study and the respiratory rate measured after excitability test. Simultanously, a significant effect of the level of nervous irritability was observed on the increase of heart rate and respiratory rate in assessed horses.