Thirty·two rats were used to compare the effects of administration of 0,7 mg/d testosterone or nandrolone phenylpropionate with the effects of presence of functional testes on growth and body composition of rats fed 20 g/rat/d of a commercial ration or of a ration of higher caloric value. Results showed that the marked effect of the presence of the testes on growth, food consumption and protein content of the carcass could not be reproduced by injection of either testosterone or nandrolone phenylpropionate into orchidectomised rats. The results indicated that some factor arising from the presence of the testes other than testosterone was the main testicular anabolic agent in the intact rat.