Summary A specific antiserum has been generated against inhibin-like material (ILM) of prostatic origin. Using the immunoperoxidase technique, localization of ILM has been examined in a total of 114 prostates including normal (4 specimens), malignant (46) and hyperplastic (55) In the present study, we report immunocytochemical localization of inhibin-like material (ILM) in prostatic tissue. Inhibin is involved in the suppression of FSH synthesis and secretion. Of the various forms of inhibin-like materials (ILM) present in human seminal plasma, a peptide having a molecular weight of 10,400 daltons has been isolated in purified form from this laboratory (Thakur et al., 1981) the amino acid sequence of which has been reported (Sheth et al., 1984a; Johnson et al., 1984;Seidah et al., 1984). This peptide-ILM has been shown to be of prostatic origin (Sheth et al., 1984b;Beksac et al., 1984) and chemically similar (Johansson et al., 1984)