Seasonal variations in the morphometric analysis of the testis, variations in testosterone production, and occurrence of pathological spermatozoa in the brown hare (Lepus europaeus) were studied. In evaluating the relative volume of germinal epithelium, interstitium and lumen in hare testis we found the highest relative volume of germinal epithelium in the winter (84.14%). The lowest level was found in the summer, but the highest relative volumes of interstitium (12.47%) and lumen (18.11%) were in the summer. The germinal epithelium achieved a maximum height in the winter (35.47 μm), when the diameter of the seminiferous tubules was also at a maximum (320.75 μm). These data are supported by analysis of testosterone production, which shows that the highest concentration of testosterone in blood was found in the winter (5.72 ng/ml), the lowest in the summer (0.87 ng/ml). This difference was significant (P<0.01). Analysis of pathological spermatozoa showed that their occurrence ranged from 11.50 to 24.17%, with the highest value in the spring. As the spermatozoa were collected from the epididymis, the most frequently found pathological form was spermatozoa with retention of the cytoplasmic drop.