The effects of prolonged androgen treatment (testosterone propionate, 10 mg/day for 56 days) on fear reactions in ewes were studied using a battery of tests previously designed and validated. These tests involved situations classically reported to induce fear in sheep: isolation from conspecifics, surprise, and presence of a human. Testosterone-treated ewes differed from controls in a number of behavioral characteristics which indicate that they are less fearful in the various test situations. Their overall scores were respectively 9.5 vs 11.5 (P < 0.05) in the isolation test, 7.9 vs 13.1 (P < 0.001) in the surprise test, and 7.8 vs 13.2 (P < 0.001) in the human test. Testosterone treatment thus clearly reduces fear reactions in ewes subjected to nonsocial situations that are typically fear-eliciting.