Immunologic potential of DA-125, a new anthracycline antitumor antibiotic, was investigated using guinea pigs and mice. In antigenicity experiments, guinea pigs were sensitized subcutaneously with DA-125 or DA-125 incorporated in complete Freund`s adjuvant (CFA) once a week for three weeks. No systemic anaphylaxis was induced by intravenous injection of DA-125 or DA-125 incubated with guinea pig serum after 3 weeks from the last sensitization. None of sera of these animals showed any passive cutaneous anaphylactic reaction (PCA) when DA-125 or DA-125 incubated with guinea pig serum was used as a challenging antigen in homologous PCA experiment. On the other hand the treatment of guinea pigs with ovalbumin incorporated in CFA induced systemic anaphylactic reaction when challenged by intravenous injection of 5 mg/body of ovalbumin. Immunodiffusion test revealed no precipitating antibodies as detected in guinea pigs sensitized with DA-125. In 24-hour heterologous PCA reaction with sera of C57BL/6 mice immunized with DA-125 or DA-125 mixed with aluminum hydroxide gel (Alum), None of sera showed positive reaction when DA-125 or DA-125 incubated with rat serum was used as a challenging antigen. Sera of animals immunized with a mixture of ovalbumin and alum showed positive PCA reaction when 5 mg/body of ovalbumin was injected as a challenging antigen. In lymphocyte proliferation tests, spleen lymphocyte proliferation to PHA and LPS was similarly impaired by 12 mg/kg of DXR or 36 mg/kg of DA-125, and the immunodepressive activity of DA-125 showed a dose-dependent manner. From these results, it could be concluded that immunosupression of DA-125 would be comparable to that of DXR and that DA-125 would not induce systemic allergic reaction in its clinical use.