Dutasteride is used in the treatment of benign prostate enlargement (BPH).It inhibits conversion of testosterone (T) into the more potent dihydrotestosterone (DHT) to stop prostate (and possibly prostate cancer) growth. DHT regulates the expression of certain genes in the prostate. The pharmacodynamics of DHT reduction in the prostate were never investigated until now, as every measurement would require prostate tissue retrieval, which is medically and ethically unacceptable. A recently developed test is able to quantitatively measure gene expression in prostate-borne cells, in urine sediments after prostate massage. By measuring this gene expression in patients using dutasteride, it has become possible to assess the pharmacodynamics of gene expression reduction, which is representative for the pharmacodynamics of DHT reduction. Repeated prostate tissue sampling has therefore become unnecessary. This newly gained knowledge will lead to a better understanding of the action of dutasteride and will possibly help improve treatment of symptomatic BPH (Benign Prostatic Hyperplasia) and PrCa (Prostate Cancer)in the future.