In the course of our screening program for new antitumor compounds, we isolated a new type of peptide, NA22598A1 (1) from a culture broth of Streptomyces sp. NA22598 (FERM P-14686). This compound proved to inhibit the anchorage-independent growth of a human colon-cancer cell line, DLD-1, on poly 2-hydroxyethylmethacrylate (HEMA) coated plates. In this paper we report the production, isolation, physico-chemical properties and biological properties of 1.