Alterations of serum immunoglobulins, especially hypogammaglobulinemia (HG), are a frequent finding in steroid sensitive nephrotic syndrome (SSNS). The exact mechanisms are unclear, especially the persistence of HG into remission. Therefore we studied serum immunoglobulins M, A and G including IgG subclasses 1-4 in 44 children with SSNS; 14 were studied during relapse (RL) and 30 in remission (RM). Data were compared with those of 23 healthy controls. In a subgroup of 23 patients (12 in RM and 11 in RL) we also studied IgG-1 specific antibodies to tetanus toxoid and IgG-2 specific antibodies to pneumococcus antigen. Increased serum concentrations of IgM in RL and reduction of serum IgG in RL and RM were confirmed. During relapse, HG was characterized to result from deficiency of IgG-1-3, whereas in early phases of relapse the reduction was due to low IgG-1 only. In RM the deficiency of IgG-2 persisted for 12 months and correlated strongly with the duration of remission ( R=0.60, P
