Acute renal failure was induced in rats by intramuscular injection of glycerol. Concentrations of intravenous 125I-labelled sodium diatrizoate were measured in plasma, renal cortex and medulla, whole kidney and in lymph nodes draining the kidney. Whole kidney concentrations of diatrizoate, which changed little with time, were initially less than 20% of those in control animals. For 30 min after injection, while plasma levels were highest, renal concentrations in acute renal failure were highest in outer cortex. These observations provide further evidence that, though glomerular filtration continues in acute renal failure, it is much reduced. Diatrizoate was observed in renal lymph nodes from control animals and its existence there does not indicate tubular leakage. Smaller amounts were found in lymph nodes in acute renal failure, suggesting insignificant drainage of diatrizoate to renal lymphatics.