In this study time for initial assessment of monthly intravenous cyclophosphamide (CP) pulse therapy is discussed for a better outcome with less complications. Eleven patients with lupus nephritis (LN) resistant to conventional therapy (serum creatinine level < or = 2.7 mg/dl) were given 500 mg/m2 of CP 7-9 times with an interval of one month. Urinary protein (Up) decreased in all patients after 3 courses of CP pulse therapy and kept similar levels thereafter. In one group of patients (n = 7), Up decreased to < 2 g/day after 3 courses, while in the other group (n = 4), it did not decrease to < 4 g/day. Creatinine clearance increased by 0-100% in the former group, while it decreased by 5-20% in the latter group after 6-9 courses. Renal function of the patients with insufficient response after 3 courses tended to show no further improvement or worsened thereafter, although Up decreased during CP pulse therapy. A relatively small dose of CP (500 mg/m2) pulse therapy was useful in most LN patients regardless of the renal histology and it was thought important to assess its effects after 3 courses for a prediction of the clinical course. Modification of the protocol at that time might be necessary in regard to dose or interval of CP administration especially for patients with insufficient outcome.