Idiopathic nephrotic syndrome in children was proposed to be a disorder of T-cell dysfunction. Though the mechanism by which T-cells increase glomerular permeability has remained elusive, cytokines released from activated Tcells have been considered to be candidates as vascular permeability factor(s). Therefore, efforts have been made to identify the pathogenetic cytokines as well as to understand the mechanism(s) for the increased release of these factors. In addition, free radicals, such as reactive oxygen species and reactive nitrogen species other than cytokines are also considered to be involved in the pathogenesis of idiopathic nephrotic syndrome. Meanwhile, recent clinical experience of remission induced by rituximab, monoclonal antibodies against B-cells (CD 20 positive cells), in refractory idiopathic nephrotic syndrome has changed our mind and B-cells have come under the spotlight as another key player. Furthermore, it is suggested that polymorphisms in the genes encoding the slit-diaphragm proteins of the glomerular barrier are contributed to the phenotype of idiopathic nephrotic syndrome. This review critically analyzes the available published data in combination with our experimental data and the emerging concept of pathogenesis in childhood idiopathic nephrotic syndrome.