The patients were randomized into 2 groups to receive either 4 mg ondansetron pIV (group O, n=86), or sodium chloride 0, 9% pIV (group C, n=84) 30 min before administration of spinal anesthesia with 0.5% hyperbaric bupivacaine, 25 mcg of fentanyl and 0.1 mg of morphine for colorectal surgery.