Serum immunoglobulin (IgG, IgA and IgM) levels were measured in 40 children with idiopathic nephrotic syndrome and 20 healthy controls. Significantly decreased IgG (P < 0.001), normal IgA and increased IgM (P < 0.05), averaging 92 per cent, 99 per cent and 104 per cent of normal mean, respectively, were observed in active nephrotic syndrome (ANS). The mean immunoglobulin levels did not differ significantly among different subgroups of ANS cases. In remission, a significant increase in IgG (P < 0.01), a decrease in IgA (P < 0.05) and in IgM (P < 0.01) levels were found in comparison to their corresponding ANS values. Their concentrations were significantly abnormal also when compared with controls. The circulating immune complexes (CIC), detected by polyethylene glycol (PEG) per cent index, demonstrated that overall mean serum level was significantly higher (P < 0.01, 168 per cent of normal) in ANS patients. Among different subgroups, the mean level was significantly elevated (P < 0.001, 205 per cent of normal) only in relapsing nephrotic syndrome cases. Thus, the abnormal levels of immunoglobulins were found both in active as well as in remission stage of the disease, while elevated levels of CIC were seen only in patients with relapse.