Seminal vesicles (SV) and coagulating glands (CG) from neonatal mice 1- to 7-days old were observed in whole mount preparations. Untreated, normal SV developed elaborate epithelial branches beginning on day 3 with secondary branches appearing on day 6. Castration (C), estradiol treatment (E), and castration combined with estradiol treatment (C + E) inhibited the morphogenesis of the epithelial branches. Untreated CG formed solid epithelial stalks that developed lateral epithelial buds on day 3 which attained a complex morphological pattern by day 7. Treatment groups (C, E, and C + E) displayed a pattern of retarded growth with few epithelial buds appearing even at day 7. The effects of castration on both SV and CG were reversed by the addition of testosterone. Short term in vitro culture of 1-day-old SV and CG glands in control medium or medium supplemented with estradiol did not exhibit visible growth. Culture of SV and CG glands with testosterone or a piece of testis showed pronounced development.