The studies were aimed at estimating the behavioural reactivity and heart rate of half-bred Anglo-Arabian stallions subjected to a novel stimulus test. The studies carried out at the Training Centre in Bogusławice involved 129 three-year-old half-bred Anglo-Arabian stallions. All the stallions were exposed to a novel optical and acoustic stimulus generated in a timidity test according to Budzyński’s method in an optical, acoustic and optical/acoustic session. Following each session of the test the stallions were rated with regard to respective types of response. They could score from 1 (high behavioural reactivit y) up to 10 points (low behavioural reactivity). Heart rate measurements were employed as a physiolo gical indicator of the level of behavioural reactivity. The heart rate of stallions was measured immediately prior to the test (initial heart rate), and then during the optical, acoustic and optical/acoustic session. To calculate the increase in the heart rate for each session, the initial heart ratewas deducted from the value measured during respective sessions. A considerable degree of nervous balance was reported for the evaluated stallions. A moving optical stimulus caused the strongest behavioural response. In response to the stimulus the highest increase in the heart rate of the stallions was recorded. A statistically signifi-cant difference was found between the mean initial heart rate and the corresponding mean rate recorded during respective sessions of the timiditytest. Stallions characterised by high reactivity in the novel stimulus test showed increased values of heart rate. Significant negative correlations between the results of behavioural assessment in the timidity test and the value of the heart rate measured during the test suggest that the novel stimulus test can be used as a fast and objective method of forecasting the suitability of horses forsafe and effective use.