Two phase II trials of mitoxantrone (Novantrone; dihydroxyanthracenedione) in refractory malignant lymphoma have been conducted. In the first of these, mitoxantrone, 5 mg/m2, was given weekly for six weeks and in the second, 14 mg/m2 was administered every three weeks. The first trial was conducted by the Southeastern Cancer Study Group (SECSG) and the second was a multicenter trial sponsored by Lederle Laboratories. Of the 51 patients entered in the SECSG trial, 28 could be evaluated for response and 43 for toxicity. WBC nadirs below 4.0 X 10(9)/litre were recorded in 25 patients. Three partial responses and no complete responses were obtained. These results contrast with those of the single dose every three weeks study in which 96 patients were entered and 69 of these were evaluated for response. Responses were obtained in 30 patients (4 complete, 26 partial). Side-effects on this three-weekly dose regimen were minimal. WBC nadirs below 4.0 X 10(9)/litre occurred in 85 patients. Twenty-three patients experienced at least mild nausea and vomiting and 15 had at least mild alopecia. These preliminary data indicate that mitoxantrone has significant activity in malignant lymphoma. All of the responding patients had received extensive prior therapy, many of them with anthracyclines in combination or as single agents. The higher response rate to mitoxantrone given at 14 mg/m2 every three weeks suggests that careful consideration should be given to dose schedule when this drug is examined further in phase III trials.