The growth and physiology of the prostate are dependent on androgens and androgen deprivation results in marked regression of the organ, which is reduced to 10% of the original size 21 days after castration. This reduction in size is caused by the loss of epithelial cell by apoptosis and prominent reorganization of the extracellular matrix. In studying the remodeling of the prostatic stroma after castration, we decided to investigate whether the activity of heparanase (HPSE), a mammalian endoglycosidase that degrades heparan sulphate proteoglycans (HSPGs), was modulated by androgens, thus contributing to the changes observed in the organ of castrated rats. For this, adult Wistar rats were subjected to orchiectomy and the ventral prostates (VPs) were collected after 7, 14 and 21 days. The VPs were processed for RT-PCR, Western blotting and immunohistochemistry assays. Western Blotting analysis showed both forms of HSPE, the active form (50kDa) and the pro-enzyme (65kDa).  The intensity of the bands were higher 7 days after castration. The enzyme heparanase was detected by immunohistochemistry at the basolateral surface of the epithelial cells and in the adjacent stroma in the control group. After castration, the labeling for HPSE increased in the stroma and was reduced in the epithelium. The highest level of heparanase mRNA, as demonstrated by RT-PCR was also observed 7 days after castration. These results suggest that HPSE is expressed in the rat ventral prostate and that its expression varies after castration. This variation in HPSE expression might be involved in the remodeling of the basement membrane, as well as in controlling the regressive pattern observed after the first week of androgen deprivation. Further studies are necessary to determine whether HPSE is directly regulated by androgens. Funded by FAPESP (Proc. 05/04004-4).