Prostatic binding protein (PBP), polyamine, and DNA synthesis were examined in primary cultures of rat ventral prostate cells. Soon after aggregates of prostate cells were placed in culture, PBP synthesis fell dramatically and DNA synthetic activity in the epithelial cells increased. The amount of polyamines that were labeled with [3H] from [3H] ornithine fell transiently, but rose again at or before the peak of DNA synthesis. Individual 3H-labeled polyamines in cells and medium were dansylated and separated by thin-layer chromatography. The ratio of [3H] Spermidine plus [3H] Spermine to [3H] Putrescine in the culture medium declined as DNA synthesis increased. Ornithine decarboxylase (ODC) activity fell dramatically along with PBP synthesis even as DNA synthesis and 3H-labeled polyamines increased in the prostate-cell cultures. These results support others that suggest that high ODC activity in prostate epithelial cells is a correlate of prostate epithelial cell function rather than proliferation. However, prostate epithelial cells retain the capacity to synthesize significant levels of polyamines from ornithine (especially Putrescine) during proliferation even when ODC activity is low.