The effect and expression of amphiregulin, a growth factor of the EGF-system was investigated in prostate primary cell cultures and in human prostate tissue. Amphiregulin increases proliferation in primary cultures of prostate myofibroblasts grown in serum-free medium. Amphiregulin mRNA is expressed in high amounts in primary cell cultures of prostate myofibroblasts, fibroblasts, epithelial cells, and in samples of prostate tissue. The data are supported by Western-blotting of amphiregulin in prostate myofibroblasts. These data call for a refocus of the expression and effects of the EGF system in the prostate.