Thirteen children with diverse forms of progressive renal disease were treated with anticoagulants, mainly heparin sodium. Increases in total hemolytic complement toward normal were consequent to treatment in four cases. Proliferative subacute glomerulonephritis of unknown etiology similar in histological appeared to that induced by nephrotoxic serum, did in two instances improve as initially proposed most likely by Vassalli and McCluskey. No significant effect was seen in more indolent renal diseases. Although no evidence for benefit to slowly progressive chronic renal disease was obtained, improvement in the two patients with rapidly progressive nephritis coincident with heparin administration would suggest that further controlled study might be of value.