A single intraperitoneal injection of hexochloro-1 : 3-butadiene (HCBD) at 100 mg/kg or above produced renal tubular necrosis in the rat by 24 h. Histological examination of the kidneys indicated damage to the straight portion of the proximal tubules. Urinary analysis showed diuresis, increased proteinuria and an increase in the excretion of N-acetyl-beta-D-glucosaminidase, and alkaline phosphatase at doses above 100 mg/kg. At doses below 100 mg/kg only a mild increase in protein excretion was observed. Twenty-four hours after 200 mg/kg HCBD, i.p., there was a marked decrease in the glomerular filtration rate (inulin clearance) and in the clearance of the organic anion (p-aminohippuric acid, PAH) and the organic cation (tetraethylammonium bromide, TEA) by the kidney. HCBD did not affect the accumulation of PAH or TEA by renal cortical slices when added in vitro at a concentration up to 0.1 mM. However, a decrease in PAH, but not TEA accumulation, was seen in renal cortical slices from rats treated with HCBD 24 h previously. Mercuric chloride (HgCl2), a known nephrotoxin, was used as a positive control for these studies. HCBD appears to specifically damage the straight portion of the proximal renal tubule and thereby selectively damage the organic anion transport system.