In 5.patients oral intake was restricted from midnight prior to operation (elective inguinal hernioplasty); in the morning urea clearance detn. was done on a 2-hr. urine specimen, and the inserted Foley catheter clamped and left in place for collection of urine during xenon anesthesia. Denitrogenation was produced by having the patient breathe O2 at a high flow; then 500-800 cc. of O2 was put in the breathing bag and the flow reduced to 250-300 cc./min.; then xenon was delivered at 900 cc./min. After about 10 min. the O2 content of the rebreathing bag was approx. 20%. This was maintained during anesthesia as determined by a Beckman O2 analyzer. Consciousness was lost when the xenon concn. reached about 50%; surgery was started when the O2 content was about 20%. Excitement during induction was absent or very mild in all but one. Xenon anesthesia was supplemented with Demerol. There was a tendency to an increase of segmented cells and decrease of serum K and plasma sugar, and bradycardia. Respiratory depression due to xenon did not occur in the concns. used. The decrease in platelet count and white blood cells in the urine were attributed to causes other than xenon.