For optimal application of new treatment strategies for prostate cancer, the basic biologic effects of androgens on cell kinetics and DNA synthesis require detailed examination. An androgen-responsive prostate cancer cell line in monolayer culture provides a means to study the biochemical mechanisms mediating hormonal stimulation of cell proliferation. We chose to evaluate the proliferative response of the Dunning R3327G tumor cell line (Du-G cells) to 5 alpha-dihydrotestosterone (DHT) in monolayer culture. The DU-G cells grew more rapidly in the presence of increasing concentrations of DHT in the range of 10(-8)-10(-5) M than with vehicle control. At 10(-7) M DHT, 3H-thymidine incorporation increased from 400 +/- 34 counts/min/well to 751 +/- 77 (p less than .01). Effects of DHT were maximal when a plating density of 10,000 cells/well was employed. Androgen effects on cellular growth were reproducible but were limited in magnitude. Rapid metabolism of DHT in culture did not explain this phenomenon. Du-G cells were not completely dependent on androgen, since cells continued to grow in media containing less than 10(-11) M dihydrotestosterone and hydroxyflutamide.