To assess the significance of remissions and relapses in idiopathic nephrotic syndrome the outcome of 169 patients was reviewed of them III had either a complete or partial remission. The probability of obtaining a complete remission within 5 years was 44% for the whole group, being significantly higher (P = 0.015) for those patients who had been treated with steroids plus cytotoxic drugs. Of the 74 patients who had complete remission only two showed renal function deterioration over time. Relapse of non-nephrotic proteinuria occurred in 22 patients. Of these, 12 again entered complete remission spontaneously, which persisted in nine until the last observation. Relapse of nephrotic syndrome occurred in 42 of III patients. Six patients showed a moderate renal function deterioration. Of 27 untreated patients, 17 had again a partial or complete remission that persisted in 13 until the last observation. All the 15 patients submitted to treatment again entered remission, which persisted in nine of 11 patients given prednisolone and chlorambucil and only in one of four given steroids alone. In conclusion, (a) the development of complete remission is a good marker of an excellent renal outcome, (b) patients with relapse of non-nephrotic proteinuria usually carry a good prognosis, (c) about half of patients with relapse of nephrotic syndrome show a spontaneous remission, and (d) the chances of a stable remission may be increased by treatment with steroids and cytotoxic agents.