Five hundred and sixteen consecutive patients have undergone upper gastrointestinal endoscopy for various reasons at the Riyadh Armed Forces Hospital, Riyadh, Saudi Arabia. As giardiasis is thought to be common in Saudi Arabia, a prospective study on these patients was carried out to evaluate duodenal aspirate and stool examination methods in the diagnosis of Giardia lamblia. Duodenal aspirate was obtained from 495 patients, but only two [0. 4%] were positive for Giardia lamblia trophozoites when examined in both wet preparation and acridine orange staining methods. Seven hundred and thirty-four stool samples from 300 patients were examined by the formalin-ether concentration method. Eight stools [1%] from six patients [2%] were positive for Giardia lamblia. Stool examination also revealed the presence of 141 other parasites in these patients