Trisodium nitrilotriacetate monohydrate was fed to male weanling Charles River rats for 28 days. Clinical evidence of urinary tract toxicity included hydronephrosis and nephromegaly. Microscopically, severe renal injury was recognized specifically as convoluted tubular cytoplasmic vacuolation and pelvic epithelial erosion. Hyperplasis occurred as a sequela to these specific cytotoxic alterations.