Carbon dioxide accumulation under ophthalmic drapes is caused by their impaired permeability to exhaled carbon dioxide in spontaneously breathing patients. Three different ophthalmic drapes were examined under clinical conditions. Sixty unpremedicated patients of each gender, aged over 60 years and with an ASA status of I-III undergoing cataract surgery under retrobulbar anaesthesia were included in the study. Patients with known pulmonary diseases were excluded. The patients were divided into three groups of 20 patients each. In all groups, oxygen was insufflated under the drapes at a constant flow of 21.min-1. Carbon dioxide concentration in the inspired air, transcutaneous carbon dioxide pressures, respiratory rate and oxygen saturation by pulse oximetry were measured. Accumulation of carbon dioxide under the drapes, increase of partial pressure of transcutaneous carbon dioxide and hyperventilation were observed in all three groups. An oxygen supply of 21.min-1 prevented hypoxaemia but not hypercapnia. Therefore, producers of ophthalmic drapes are encouraged to look for further ways to increase the carbon dioxide permeability of their drapes with the aim of reducing carbon dioxide accumulation and hyperventilation in spontaneously breathing patients undergoing eye surgery.