Of 61 boys and girls with relapsing or steroid-resistant nephrotic syndrome admitted for renal biopsy, 22 had persistent hepatitis B virus surface antigenaemia despite normal liver function and an absence of previous transfusion. The prevalence of hepatitis B virus surface antigenaemia amongst nephrotic patients is significantly higher than that of the general population. Membranous nephropathy remains the commonest glomerulopathy associated with hepatitis B virus antigenaemia, and boys predominate.