We present a patient with steroid-sensitive but high-dose steroid-dependent nephrotic syndrome who was treated with rituximab. For 9 months following therapy she had undetectable CD19 cells in the peripheral circulation. She remained in remission during this period even though therapy was reduced to low-dose, alternate day prednisolone only. After 9 months, CD19 cells were once again detectable. Shortly after CD19 cells became detectable again she relapsed. We conclude that B-lymphocytes play a central role in the pathogenesis of idiopathic minimal change nephrotic syndrome (MCNS) and that rituximab may have a useful role in the management of steroid-dependent patients.