Studies on the developing prostate and SV suggest that androgens act via mesenchymal AR to elicit synthesis and secretion of various autocrine and paracrine factors that regulate epithelial and stromal growth and differentiation. Clearly, the global regulation of epithelial growth and ductal branching morphogenesis is a complex multifactorial process involving the interplay of many diffusible factors (both positive and negative regulators), extracellular matrix molecules, cell-surface receptors for growth factors, receptors for extracellular matrix molecules, and matrix-degrading enzymes. Future progress will certainly be dependent upon the utilization of appropriate, biologically relevant models to examine the respective roles of various growth factors in the growth and development of androgen target organs.