Numerous examples of abnormal immune responsiveness have been described in minimal change nephrotic syndrome (MCNS). The of MCNS with allergy and with certain genetic markers of immune responsiveness, as well as the excellent response of proteinuria to immunomodulatory agents, has suggested a causal relationship between the immunological and renal abnormalities. However, the nature of this relationship is uncertain. Before it can be clarified, the basic mechanism(s) involved in disturbed immunity in patients with MCNS must be better characterized. Studies of humoral and cellular immune function support the hypothesis that immune regulation is abnormal. However, conclusive evidence of participation by a defined immunoregulatory system in the events leading to immune dysfunction has not been obtained. Thus, considerable work remains to be done in determining the nature and cause of abnormal immunity in MCNS prior to investigating its potential role in the pathogenesis of proteinuria.