Forty Dorper ram lambs were allocated to two trails. In the first trial (intensively housed) and second trial (extensively maintained), one group (n + 10) in each trial was treated weekly with an intramuscular injection of an anabolic steroid (50 mg nandrolone laurate) for a 12-week period. The other group (n = 10) in each trial served as a control. Several body parameters were measured during this treatment period and monitored for an additional 12-week period. In the intensively and extensively housed groups, treatment with the anabolic steroid did not significantly increase the growth rate when compared to the controls. There was, however, a significant (p < 0.01) difference in ADG and final body weight between intensive and extensively housed animals. Shoulder height (66.3 vs 66.6 cm and 65.0 vs 66.5 cm); shoulder width (29.7 vs 28.0 cm and 19.0 vs 19.3 cm); bodylength (85.9 vs 86.0 cm and 74.5 vs 75.4cm); cannon bone diameter (2.4 vs 2.2 cm and 2.1 vs 2.0 cm); serum testosterone concentration (1.15 ± 0.97 vs 2.21 ± 0.83 ng/ml and 0.15 ± 0.1 vs 0.89 ± 0.58 ng/ml) and FCR (measured only in the intensively housed animals) (7.6 vs 9.4) did not differ significantly between the treated and control animals over the entire observation period for the intensive and extensively housed animals respectively. No significant difference in semen quality was recorded in the intensively housed animals from 3 months following treatment. Scrotal circumference was significantly (p < 0.01) less in the treated groups (intensive and extensive groups) during the treatment phase, when compared to the controls, with a decrease of 9.5% and 18.4% respectively. Scrotal circumference recovered and increased during the recovery phase. Although use of the anabolic steroid did not result in a significant increase in growth rate (intensive and extensive conditions), it would seem that nutrient availability (metabolisable energy) affected the response. With higher energy diets, a better ADG and FCR could possibly have been attained. The androgenic effect of the steroid treatment retarded testicular development, but this phenomenon was temporary and fertility was normal (when compared to the controls) by 12 weeks following treatment.