Fifteen patients with a primary myelodysplastic syndrome (MDS) transformed into acute myeloblastic leukemia (AML) were treated with an intensive chemotherapy regimen containing idarubicin. A complete response (CR) was obtained in 10 patients (66.6%). In five of them this was achieved after a single course of chemotherapy. The median time to achieve a CR was 32 days (range 16-42). A partial remission (PR) was obtained in 2 patients after two induction courses of chemotherapy. One patient died during the first induction course following acute respiratory distress syndrome (ARDS) complication, whereas the chemotherapy regimen failed in 2 patients. A short interval between MDS and transformation into AML was associated with a better chance of achieving a CR. Age, karyotype, type of MDS, peripheral blood or bone marrow findings appeared to have no influence on the response to treatment. The median event free survival for patients who achieved CR was 15 months and the median actuarial survival 18 months. These preliminary results need to be confirmed in a multicentre prospective study comparing idarubicin with other anthracyclines.