Administration of mercuric chloride (HgCl2, 6 mg/kg) to rabbits produced renal failure, with changes in serum creatinine from 1.01 ± 1 in controls to 6.46 ± 0.91 mg/dl 24 hr after administration. Mitochondria isolated from HgCl2-treated rabbits exhibited alterations in acceptor control ratios, with reduction to 1.9 ± 0.2 from 3.9 ± 1.2 in controls. Ultrastructurally, the mitochondria showed swelling and loss of inner mitochondrial membranes. Total lipids from mitochondria of control and treated rabbits were obtained by modified Folch extraction and phospholipids analyzed by TLC. Brush border membranes and basolateral membranes were prepared from control and HgCl2-treated kidneys 2 and 24 h after HgCl2 administration. At 24 hr mitochondria showed a 36% fall in phosphatidylcholine (PC), a 36% fall in phosphatidylethanolamine (PE), and a 27% fall in cardiolipin. Brush border showed a decrease in phosphatidylserine (PS) of 29% and in PE of 40%. The basolateral membranes showed a reduction only in PE of 35%. At 2 h post HgCl2, early changes are confined to the BBM and consist of a reduction in PE in this membrane. This changes in membrane phospholipids may be important in the functional derangements that occur at the cellular level after HgCl2 administration.