19-nortestosterone cyclopentylpropionate (NTCP) has been found to have 20% of the activity of testosterone propionate in stimulating the seminal vesicle of the castrate rat and to have nearly twice the activity of testosterone propionate in causing growth of the levator ani muscle. The present study describes semi-quantitative measures of the ability of this compound to cause retention of nitrogen in adult castrate male rats force fed a constant intake of medium carbohydrate diet Comparison with testosterone propionate (TP) in 30-day courses of injection revealed that 0.5 mg. per day NTCP produced a greater nitrogen-retention response than 0.25 mg. TP but a lesser response than 1.0 mg. TP; 2.0 mg. NTCP produced the same response as 0.5 mg. NTCP. NTCP at a daily dose of 0.25 mg. caused greater nitrogen retention than did androstanolone (17[beta] -hydroxy androstane-3-one) or methylandrostenediol (17 a -methyl 45-androstene-3 fl, 17 0-diol) at daily doses of 2.0 mg. A single injection of 2 mg. of NTCP caused significant retention of nitrogen lasting several days, while a similar injection of 19-nortestosterone did not produce significant retention.