For the present work, cultures of hyperplastic human prostate explants were performed to evaluate the "in vitro" response of a 5-alpha reductase inhibitor-finasteride. Explants were cultured over a nine-week period in RPMI-1640 media supplemented with Penicillin-Streptomycin 4% and Fetal Bovine Serum 10%. Cultures were divided into one control group, one with testosterone added (1.25 x 10(4) micrograms/ml) and one which received testosterone (1.25 x 10(-4) micrograms/ml) plus finasteride (0,0038 mg/ml). Control explants showed involutive changes throughout the experience, which occurred later in those treated with testosterone and earlier and more marked in the case of finasteride. The testosterone-treated group showed intense positivity for PSA, a marker which reveals specific tissular functions, which remained uniformed in the control group through the entire experiment, and decreased gradually in the finasteride group. In summary, according to our work, culture of organs would be a useful tool for an in vitro evaluation of the hyperplastic human prostate response to the action of the 5-alpha reductase inhibitor, finasteride.