40 patients with idiopathic membranous glomerulonephritis were randomized to receive either no treatment or a regime of cyclophosphamide for 6 months, and warfarin and dipyridamole for two years. During the two years of the trial there was no significant deterioration in renal function in either group. A significantly greater improvement in urinary protein excretion was, however, observed at all time points in the treatment group. Plasma albumin was also significantly higher in the treatment group at 18 and 24 months. As progressive deterioration in renal function in membranous glomerulonephritis is associated with persistent heavy proteinuria these results suggest a beneficial effect of treatment.