Tissue recombinants of epithelium and stroma from embryonic and neonatal urogenital rudiments derived from wild-type and feminized (Tfm/Y) mice sere grown as grafts in intact male hosts and analyzed morphologically for androgenic response. When mesenchyme of embryonic wild-type urogenital sinus (UGS) was associated with epithelium from embryonic wild-type bladder (B), the epithelium developed into glandular structures resembling prostate. In the reciprocal recombinant (B mesenchyme + UGS epithelium) the response was mixed, half of the recombinants exhibited bladder morphology and half exhibited prostatic-like morphology. Vaginal-like histogenesis occurred in UGS recombinants of androgen-insensitive Tfm/Y mesenchyme and wild-type epithelium, while prostatic morphology developed in reciprocal recombinants of wild-type mesenchyme and Tfm/Y epithelium. These observations demonstrate (1) that the presence of wild-type mesenchyme appears essential for expression of androgen-dependent morphogenesis during embryonic periods; and (2) that Tfm/Y epithelium is capable of participating in an androgenic response. Conversely, in similar recombinants prepared with neonatal tissues, the presence of wild-type urogenital stroma may not be required for expression of certain androgen-dependent phenomena since maintenance of the height and cytodifferentiation of ductus deferens epithelium occurs even when this epithelium is associated with Tfm/Y urogenital stroma. It appears, therefore, that the requirement of urogenital epithelium for wild-type (androgen sensitive) stroma may vary temporally.