We previously used autoradiographic methods to show that cells proliferate throughout the rat ventral prostate during its postnatal development (Biol Reprod 1991; 45:773-782). The objective of the present study was to quantify the extent to which DNA synthesis, and thus growth, occur in the distal and proximal segments of the rat ventral prostate. To this end, rats were administered 3H-thymidine in vivo. Subsequently, 3H-thymidine incorporation per prostatic segment and per micrograms DNA was determined, as was the number of labeled cells in the proximal and distal segments. We report that 3H-thymidine was incorporated into both the distal and proximal segments of the ventral prostate of rats 10, 20, 45, and 60 days of age, with significantly greater amounts (6-21 times) incorporated into the distal segment at each age. Consistent with this, the distal segment contained 5-20 times more labeled cells than the proximal segment. However, when 3H-thymidine incorporation was expressed per micrograms DNA, only relatively small, though significant, differences were seen between the distal and proximal segments of Days 10 and 20; and no differences were seen at Days 45 and 60. Taken together, these results strongly support the contention that DNA synthesis occurs throughout the rat ventral prostate, and suggests therefore that prostatic growth is not limited to the distal tips of the gland.