Epithelial cells from human benign prostatic hyperplasia tissues were grown in primary cultures for up to 21 days and the effects of interferons on the growth of the cells were investigated. Interferon-alpha (Wellferon) showed growth inhibition both in the presence and in the absence of 3 x 10(-10)M testosterone propionate (TP) whereas interferon-gamma stimulated growth in a dose dependent manner under similar conditions. Interferon-beta had little effect on growth at the dose levels used in the study. The growth inhibition by interferon-alpha can be induced after stimulation of growth is achieved either with TP or with interferon-gamma. Implications of these findings for clinical use of these lymphokines is discussed.