Murine erythroleukemia cells established by Friend et al. are transformed cells blocked in erythropoesis differentiation and serve as a useful model for investigating regulated expression of specialized cell functions. In our screening program for inducers of Friend leukemic cell differentiation, we isolated an active substance 145-A, identified as trichostatin C (an antifungal antibiotic) via ¹H-NMR, IR, UV spectral data, ¹³C-NMR comparison with authentic trichostatin C, and direct sample comparison. Trichostatin C potently induced differentiation of Friend leukemic cells (DS-19) at a concentration range of 100-400 ng/ml (0.2-0.8 μM), with approximately 80% of cells differentiated within 5 days at the optimum concentration (250-300 ng/ml). It also induced Rausher virus-transformed mouse erythroleukemic cells (RV133) into benzidine positive cells at a similar concentration. Compared to other inducers (e.g., chaeotropic agents like HMBA and DMSO requiring high concentrations, or DNA-attacking agents with weak efficiency), trichostatin C characteristically induces erythroid differentiation with high efficiency at a very low concentration. Further studies on the mechanisms of its potent inducing activity are in progress.