A pilot study of 21 patients (17 women; 4 men; mean age 35 [18-59] years), randomized into two groups, was undertaken to test how many cycles of intravenous pulse cyclophosphamide administration were required in lupus nephritis to achieve remission. It was planned that patients randomized to group A should be treated for 3 months, those in group B for over 12 months. In the first cycle the cyclophosphamide dosage was 500 mg/m2, in the subsequent cycles, 4 weeks apart, it was raised by 250 mg/m2 to a maximum of 1,000 mg/m2, if the WBC count was over 2,000/microliters. Three women in group B gave up treatment prematurely after 5-8 cycles, because a remission had occurred. In group A only one patient went into remission after only three cycles. Of the total of 18 patients in both groups whose data could be evaluated, 15 achieved remission after an average of 7.3 cycles and a cumulative total cyclophosphamide dosage of 9.3 g. The disease progressed in two patients, one died. No recurrence has so far been observed after a follow-up period of 1-41 months. Three patients had infections and two had developed leukopenia as side effects. Pulse cyclophosphamide has thus been shown to be an effective treatment in lupus nephritis, but it must be continued for more than 3 months.