OBJECTIVES To study changes in kidney function immediately after abdominal or eye surgery and to assess the roles of vasoactive substances: antidiuretic hormone (ADH), renin and aldosterone and natriuretic factors (atrial natriuretic peptide [ANP] and digoxin-like immunoreactive factor [DLIF]) in renal function. PATIENTS AND METHODS We distributed 23 patients into 2 groups. Group A contained 16 subjects undergoing high abdominal surgery (cholecystectomy) under general anesthesia, and group B included 7 patients undergoing cataract extraction and intraocular lens implantation with peribulbar anesthesia. The first blood sample was taken before anesthetic induction; the first urine sample had been taken 24 hours prior to surgery. The second blood and urine samples were taken 2 hours after the patient's arrival in the intensive care recovery ward. RESULTS Patients undergoing abdominal surgery experienced significant decreases in diuresis (p < 0.01) and sodium excretion (p < 0.05) and increases of potassium in urine (p < 0.01) and urinary osmolarity, accompanied by high ADN (p < 0.01) and aldosterone (p < 0.01) levels in both blood (p < 0.05) and urine. Renin, ANP and DLIF did not change significantly in patients receiving peribulbar anesthesia. CONCLUSIONS The increases in ADH and aldosterone levels that occur as a response to stress in abdominal surgery are implicated in the antidiuretic and antinatriuretic effects observed in the postoperative period. Renin, ANP and DLIF do not seem to be responsible for kidney dysfunction.