Until now, literature data support the fact that the CHOP regimen represents the standard first line treatment for patients with advanced intermediate-grade non-Hodgkin's lymphoma. Recently, idarubicin has been introduced in clinical trials because of its favourable preclinical profile: it is more active than daunorubicin and doxorubicin against a number of experimental tumour systems and is significantly less cardiotoxic in animal models. From March 1991 to June 1993, 115 previously untreated patients with stage II to IV intermediate-grade non-Hodgkin's lymphoma, according to the Kiel classification, were enrolled in a phase III comparative trial. The objectives of the study were to compare the efficacy and safety of using idarubicin instead of doxorubicin in the polychemotherapeutic regimen CHOP (cyclophosphamide, doxorubicin, vincristine, and dexamethasone). Of the 115 patients registered for the trial, 103 were evaluable: 52 received CH (doxorubicin)OP and 51 received CI(Idarubicin)OP. Known prognostic factors were equally distributed among the two groups. There were no significant differences between the 2 groups in the rates of partial and complete response. The overall response rate was 87%, with complete response in 62%: 63% in the CHOP group, and 59% in the CIOP group. At 30 months (median 20 months), 86% of all CR patients were alive without disease in the CHOP group and 85% in the CIOP group. Patients treated with CHOP experienced severe alopecia more frequently (P = .004). Only three patients in the CIOP group showed cardiac adverse events (1 moderate and 2 mild), while in the CHOP group 4 mild, 2 moderate and 1 severe were recorded. LVEF monitoring was carried out in 31 patients of the CHOP group and in 27 of the CIOP group. A median drop of 8.3% of the LVEF was observed in patients treated with CHOP regimen as compared to 4.8% in patients with CIOP regimen (P = .0001). In this trial, the "idarubicin arm" (CIOP regimen) was found to have an equivalent therapeutic efficacy and, slightly, reduced clinical toxicity in comparison to the standard doxorubicin-containing CHOP regimen in patients with intermediate-grade non-Hodgkin's lymphoma.