Two cases of childhood nephrotic syndrom (NS) were diagnosed in September 1981 and February 1982, respectively. The patients were first cousins. There was no other family history of renal disease. Five months after onset of nephrosis in 1 patient and 1 month after onset of nephrosis in the other both had an intercurrent measles infection and the NS rapidly went into spontaneous remission. However, relapses occurred 3 and 7 months later. At that time both patients were started on steroid treatment and obtained remission. Unfortunately, both relapsed again 14 months later. Kidney biopsies were performed, the pathologic findings demonstrated that both were mild mesangial proliferative glomerulonephritis. The mononuclear cell subsets and lymphoproliferative responses were studied during the acute measles infection, 4 weeks later, in remission and relapse of NS. The mononuclear cell subsets and lymphoproliferative response in medium containing autologous serum with complement were decreased during the acute measles infection. Both patients had an increase of OKT8 cells and Leu-7 cells in relapse and a decrease in remission. Taken together, natural measles infection caused a prolonged depression of cell-mediated immunity, T cell subset and induced a temporary remission of steroid-sensitive NS.