Plasma factor VIII procoagulant activity has been shown to be significantly elevated in 32 children with the nephrotic syndrome. This increase is more marked in those with obvious glomerular lesions on histology than in patients with minimal change nephropathy. Fluctuations in factor VIII levels corresponded to changes in the clinical condition of the nephrotic syndrome. In 28 children with post-streptococcal glomerulonephritis, 4 patients with the highest factor VIII levels recovered between 7 and 60 days of onset of disease whereas the remainder did so in less than 7 days. Factor VIII levels may reflect the extent of immunopathological injury to glomerular capillaries and be useful in management of children with glomerular disease.