The Stanley-Gumbreck male pseudohermaphrodite (Ps) rat has a generalized end organ insensitivity to testosterone. The retention of testosterone- 3H and its 5α-metabolite, dihydrotestosterone, by preputial gland nuclei from these Ps and normal male rats was compared. Although total intranuclear radioactivity was similar in both types of animals, its distribution between the two steroids was distinctly different. Nuclei from normal rats concentrated primarily dihydrotestosterone while nuclei from the androgen insensitive animals retained testosterone. The inability of nuclei from Ps rats to concentrate dihydrotestosterone may explain the androgen insensitivity in these animals.