Objective: To determine whether human fetal urogenital sinus mesenchyme (UGM) can induce prostatic development in a responsive mouse epithelium. Method: Male and female human fetal UGM was combined with mouse urinary bladder epithelium (BLE), and the resultant human UGM+ mouse BLE tissue recombinants were grown under renal capsules of male athymic mice. Human male and female UGM was derived from reproductive tracts 9 and 14 weeks of gestation obtained following elective termination of pregnancy. At these ages prostatic ducts had already emerged from the urogenital sinus epithelium, and the human UGM remained contaminated with human prostatic epithelium. This unavoidable problem was tolerated because the induced mouse prostatic epithelium could be distinguished from contaminating human prostatic epithelium. Results: The simple columnar epithelium induced from mouse bladder epithelium by human male and female UGM resembled mouse prostatic epithelium by:(a) histology,(b) the pattern of basal cell distribution,(c) Hoechst dye nuclear staining,(d) expression of NKX3. 1,(e) the pattern of androgen receptor expression and (f) the expression of probasin, a mouse prostatic secretory protein. Summary/Interpretation: These findings provide validation for mouse as a model of human prostatic development as the molecular dialogue involved in mesenchymal-epithelial interactions are sufficiently conserved that human UGM can induce mouse bladder epithelium to undergo prostatic development.