Fifty-five patients scheduled for relatively short (1-2 hours) elective surgical procedures were divided into methoxyflurane and control groups. In both groups the potent inhalation agent used, methoxyflurane or halothane, was administered in the smallest amounts compatible with adequate anesthesia. Renal function was assessed by preoperative and postoperative measurements of serum urea, creatinine, sodium, and osmolality and urinary creatinine and osmolality and by calculation of creatinine, osmolar, and free-water clearances. In ten patients in each group serum and urinary fluoride levels were determined pre-and postoperatively. In addition, serum fluoride levels of 33 patients who had received methoxyflurane for vaginal deliveries were measured postpartum. No clinical or laboratory evidence of renal dysfunction was observed, and fluoride levels were markedly lower than those previously associated with renal toxicity.