Endotoxins (lipopolysaccharides; LPS) are known to cause multiple organ failure, including renal dysfunction. The present report elucidates LPS distribution and effect on renal proximal tubules in an attempt to gain a better understanding of the cellular mechanism underlying the pathogenesis of renal dysfunction in endotoxemia and sepsis. Rats were intravenously treated with biotin-linked or regular Escherichia coli (0111:B4) LPS (3 mg/kg) and sacrificed at different times. Kidneys were retrieved and examined for LPS localization, tubular permeability, ultracytochemical alterations, leukocyte sequestration, and ICAM-1 expression. The functional impact of endotoxemia was also assessed by monitoring the changes in urine levels of glucose in timed collections up to 6 h. LPS was localized on the plasma membranes of the apical microvilli, the labyrinth of the lateral intercellular spaces, in various organelles of epithelial cells, and in the endothelial cells of the peritubular capillaries. LPS caused structural damage and calcium accumulation in the mitochondria, leakage of tight junctions, widening of the basolateral intercellular spaces, intracellular and extracellular edema, leukocyte margination and accumulation, vascular expression of ICAM-1, and decrease of plasma membrane and mitochondrial Ca2(+)-ATPase. Physiological study showed that both urine volume and glucose were greatly increased after LPS infusion. The pathological alterations in the proximal tubules may directly contribute to the reduction in the reabsorption ability of the proximal tubules.