Normal prostate glands from 6 men less than 30 years old and enucleated tissue of benign prostatic hyperplasia were analyzed by stereological methods. Studies on the relative volumetric amount of fibromuscular (stromal) and glandular areas of the gland reveal no statistically significant difference between the inner and outer parts of the normal prostate and between the inner part of the normal prostate and benign prostatic hyperplasia. However, in benign prostatic hyperplasia there is a significant increase in the volumetric amount of the fibromuscular tissue and a decrease in the glandular area compared to the outer part of the normal prostate and the whole normal prostate (sum of the inner and the outer parts). These stereological data are discussed with respect to the pathogenesis of benign prostatic hyperplasia.