Résumé : In an effort to characterize the hormone sensitivity of human benign prostatic hyperplasia (BPH) maintained in organ cultures for 12-72 h, the influence of 5-alpha-dihydrotestosterone (DHT), testosterone (T), 17-beta-estradiol (E2), progesterone (Pg), or prolactin (PRL) was assessed on the cell proliferation rate of 25 BPH specimens by the use of tritiated thymidine incorporation followed by autoradiography. Significant increases in the thymidine-labeling index (TLI: percentage of labeled nuclei) were observed in glandular tissue after a 36-h incubation period in presence of DHT, E2, Pg, or PRL in 52%, 44%, 28%, and 60% of BPH cases, respectively. Nonparametric statistics (Spearman and Kendall rank correlation tests) have shown that 1) the steroid-induced TLI increases are dependent on the basal rate of cell proliferation, while the PRL-induced effect is independent of it, and 2) all the steroid-mediated effects on BPH TLI are correlated together, whereas they seem to be independent of the PRL-induced TLI increase. When T was compared with DHT on nine BPH specimens, three were found to be sensitive to both hormones, and two responded to DHT only. We propose that our study methods are suitable as a means to assess the hormone sensitivity of individual cases of BPH and possibly prostatic tumors.