It is well established that androgens are central to regulation of the growth of the mammalian prostate gland. Conversely, androgen deprivation by castration induces rapid cell death in the ventral prostate via an apoptotic mechanism. To date, most studies of cell death in the rodent prostate have focused on the ventral lobe, with little attention directed to the dorsal and lateral lobes. The results presented herein demonstrate that cell death in the rat prostate gland caused by castration is lobe specific. In particular, castration caused decreases in wet weights and protein contents of all three prostatic lobes, but these events were more rapid and profound in the ventral than in the dorsal and lateral lobes. Reduced epithelial cell size was apparent in the three lobes as well. However, castration resulted in loss of DNA content in the ventral lobe only. To confirm this finding, and to examine apoptosis of individual cells, we used in situ labeling of fragmented DNA, supported by biochemical analysis of DNA integrity in agarose gels. With both approaches, significant cell death in response to castration was seen in the ventral lobe but not the dorsal and lateral lobes. Taken together, these results clearly indicate that there are lobe-specific differences in the response of the rat prostate to androgen ablation by castration, with apoptotic cell death occurring in the ventral lobe of the prostate but to a far lesser extent, if at all, in the dorsal and lateral lobes. Moreover, castration caused apoptotic death of both epithelial and stromal cells of the ventral prostate, with these cells dying throughout the ductal network of the ventral prostate rather than being restricted to a particular region. We suggest that lobe-specific differences in androgen responsiveness in the rat prostate may provide an appropriate model for the study of androgen-independent prostatic cell survival during tumor progression.