Immature tiger salamander larvae were treated with 12.5 or 25 μg of estradiol, testosterone, or dihydrotestosterone (DHT), or 12.5 μg of estradiol combined with 12.5 μg of either testosterone or DHT. Mullerian duet epithelium was more stimulated by combined steroid treatment than by any steroid alone. Estradiol antagonized the action of DHT in the Wolffian duct. Both of the androgens and estradiol when administered alone at the higher dose stimulated enlargement of connective tissue surrounding the ducts, but the combined 12.5 μg androgen/12.5 μg estrogen treatment was more effective even though the total steroid administered was the same. The effectiveness of DHT on Mullerian cells of this species is evidence against a required aromatization of androgens to explain paradoxical steroid effects and suggests that fundamental differences may exist in steroid receptors of Mullerian ducts, connective tissue, and Wolffian ducts. A possible role for the urodele duct system for assessing estrogenic activity of environmental contaminants is discussed.