Growth factors, as detected by DNA synthesis stimulating activity for BALB/c 3T3 cells, in normal, benign hypertrophic and cancerous human prostates were analyzed. The total content (units per gram of tissue) in benign hypertrophic prostate was two to four times higher than those in normal and cancerous prostates. In all the three groups, heparin-binding growth factor, growth factor adsorbed to heparin-Sepharose in the presence of 0.5 NaCl. accounted for about 80-95% of the total growth factor content. Qualitative analysis using a heparin-Sepharose column revealed two types of heparin-binding growth factor in the prostates, one eluted from the column at 1.2-1.3 M NaCl and the other at 1.5-1.8 M NaCl. The latter was the predominant type in all groups. In addition to the growth factors detected with BALB/c 3T3, a growth factor with specific action upon MC3T3-E1 mouse osteoblasts was found in prostatic cancer, but not in normal and benign hypertrophic prostates.