Animals maintained on retinol (vitamin A-alcohol)-deficient diets exhibit testicular atrophy and loss of the germinal epithelium. Retinoic acid (vitamin A-acid), when fed to retinol-deficient animals, does not prevent these lesions and had thus been thought not to play a role in the tests. Serum testosterone (T) levels, determined by RIA, in retinol-deficient rats were determined to be significantly lower than in control rats. In contrast, retinoic acid-fed, retinol-deficient rats exhibited serum T concentrations similar to those of control rats. No difference in immunoreactive serum LH levels was observed in the three groups. The response of serum T to ip administration of LH in retinol-deficient animals relative to basal levels was similar to that observed in control as well as retinoic acid-fed, retinol-deficient rats. These results show that while basal T production in retinol-depleted rats is decreased, LH-stimulated T synthesis is unaffected. Furthermore, retinoic acid, in the absence of retinol, can support T production, suggesting that contrary to present dogma, retinoic acid plays a role in testis.