Four patients who presented with severe proliferative glomerulonephritis associated with linear deposition of IgG on the basement membrane have been treated by intermittent massive plasmapheresis. Two patients had all the features of Goodpasture's syndrome. In the other two cases, the characteristic renal lesion was present but there was no pulmonary involvement. In all cases, renal function improved after plasmapheresis while in two, renal function deteriorated after plasmapheresis was stopped. On of these patients responded to a second course of plasmapheresis but failed to respond to a third. This study supports previous reports of the value of plasmapheresis in patients with Goodpasture's syndrome and renal failure in whom recovery without plasmapheresis has not been recorded. The present study emphasizes the importance of continuing treatment for a period of weeks to permit prolonged remission. If treatment is withdrawn too early, rapid deterioration in renal function may result, and unless plasmapheresis is recommenced at once the renal failure may then prove irreversible.