Between 1971 and 1981, 74 patients with polycythemia vera were treated with pipobroman using a high-dose induction, low-dose maintenance regimen. Complete remission was achieved in 51 of 54 previously untreated patients (94.4%) and in 17 of 20 patients (85%) previously treated wih radioactive phosphorus (32 p) and busulfan. The earliest modifications were noted on day 16, and on the average, blood counts were normal by day 45. Thirty percent of the patients relapsed, the mean duration of the remission being 17.5 mo. Following recurrence pipobroman was consistently effective in the same doses but the mean duration of the next remissions was 10 mo. Transient leukopenia and thrombocytopenia occurred in 8% and 7% of patients, respectively, during initial phase, and anemia was noted in 3 patients. Macrocytosis was noted in 20% of patients during maintenance phase. Three cases of acute leukemia and 3 cases of osteomyelosclerosis were recorded, all occurring in patients who had previously received 32 p and/or busulfan. No hematologic malignancies were seen among patients treated with pipobroman alone; follow-up exceeded 6 yr for 20 patients and the median follow-up period was 3.6 yr. Pipobroman appears safer than other alkylating agents; it is as effective as 32 p and works more quickly. Longer follow-up will be required to evaluate the drug's oncogenic potential, which is still not known.