To find out if determination of factor VIII,which most probably is synthetised in the intima of blood-vessesls, is of value for predicting the severity of vessel damge in glomerulonephritis, factor-VIII activity, factor-VIII-related antigen, and glomerular filtration-ratewere esto,ated om 85 patients with early glomerulonephritis on admission, and in 70 of these at follow-up for up to 4 years. The levels of factor-VIII activity and factor-VIII-related antigen on admission were normal in those patients who recovered. Where renal function was impaired on admission or becaome so during follow-up, factor VIII was high. Determination of factor VIII might thus be of prognostic value in early glomerulonephritis.