Four patients who had ingested large amounts of phenacetin-salicylate medications were studied during a 12-month period. Renal failure had progressed slowly over a number of years. All patients took the drug because of psychogenic headache. Considerable skill was required to elicit the history of drug habituation. The major features of the nephropathy were multiple episodes of metabolic acidosis, minimal proteinuria, pyuria but no bacteriuria, and polyuria and polydipsia early in the course of drug ingestion. Papillary necrosis was not a prominent clinical feature of this series. Discontinuation of drug ingestion by one patient was associated with recovery of a considerable degree of renal function. Preliminary experimental evidence obtained in the dog suggests that salicylate impaired the efficiency of the counter-current multiplier by decreasing sodium transport in the ascending limb of Henle, and decreased the permeability to water of the distal convoluted and collecting tubule; phenacetin had no such effect.