Thirty-six weaned male NZW rabbits (35 days of age) were used in the present study. The animals were divided into two experimental groups (18 each group). The animals in the first group were injected bi-weekly with 0.5 ml testosterone during the period from weaning up to 4 months of age. The second group was injected with saline solution (control). Growth performance, gonadal development and reproductive efficiency were studied during summer months. Live body weight, daily gain weight and feed conversion were improved insignificantly following testosterone injection. Histological studies showed full complement of germinal elements in the testosterone injected males as compared to the control. The differences between the two experimental groups in plasma testosterone concentrations were not significant. Sperm motility and sperm concentration increased (P less than 0.01), while abnormal and dead spermatozoa decreased (P less than 0.05) in the treated animals as compared to the control. However, the ejaculate volume was insignificantly different between the two experimental groups. The effect of month on each of sperm motility and abnormal spermatozoa was significant (P less than 0.05). The lowest percentages of sperm motility and the highest percentages of abnormal spermatozoa were recorded during July. The interaction effects between testosterone injection and summer months on semen characteristics was not significant. Conception rate was insignificantly higher in the does mated with testosterone treated bucks. Litter size at birth was significantly (P less than 0.05) increased in the does mated with testosterone treated bucks, while litter size at 21 and 30 days of age (weaning age) showed insignificant differences between the two experimental groups. Conception rate and litter size at different ages were insignificantly higher during June as compared with July and August months. The interaction effects between testosterone treatment and month of kindling on fertility traits were not significant.