In vitro studies suggest that the protease activity of PSA might play a functional role to facilitate the growth and spreading of cancerous prostatic cells. hK2 may have similar properties. Further investigation to prove their in vivo effects is required. Regulation of PSA and hKLK2 gene expression is mediated not only by androgens, but also by a number of autocrine and paracrine factors, suggesting that the control mechanisms for expression of these genes are complex and multifaceted. Such factors may also be integral for the growth and differentiation of prostate cells. Thus PSA and hKLK2 may serve as useful markers to study the regulation of gene expression during cell growth and differentiation of the prostate.