Atopic systems were more common in children with steroid-responsive nephrotic syndrome (S.R.N.S.) than in matched controls, and HLA-B12 was more common in children with S.R.N.S. than in adult controls. Atopic symptoms (particularly hayfever), positive prick tests with grass pollen antigens, and a higher mean serum concentration of IgE antibody to timothy grass pollen were more common in nephrotic children with HLA-B12 than in those without HLA-B12. There was also an increased frequency of the haplotype HLA-A1 and HLA-B8, mainly among the non-atopic patients.