A late phase II study of idarubicin hydrochloride combined with vincristine and prednisolone was conducted in adult patients with acute lymphocytic leukemia (ALL) in the first relapse as a multi-center joint research project. The dosages used were idarubicin 12 mg/m2/day i.v. for 3 consecutive days (day 1-3), vincristine 1.4 mg/m2 i.v. (day 1) and prednisolone 60 mg/m2/day po for 5 consecutive days (day 1-5). The number of evaluable patients was 20. The patients showed responses including 3 complete remissions (CR) and 10 partial remissions (PR), with an efficacy rate (CR + PR) of 65.0%. Adverse reactions occurred in 19 of 20 patients. The main symptoms were gastrointestinal symptoms including anorexia, nausea/vomiting, and stomatitis and fever, infection, and alopecia. Abnormal laboratory data were observed in 6 of 20 patients with 13 events. Although one case of an increase in GPT with WHO grade 3 was observed, the other cases were not of significance. From the above study, idarubicin hydrochloride was considered to be effective in relapsed ALL patients in combination therapy with vincristine and prednisolone.