The effects of polyethylene glycol (PEG) on gastric function and on lesion formation, evoked by topical applications of absolute ethanol to an ex-vivo stomach chamber preparation have been examined. Parenteral injection (i.p. or s.c.) of PEG with different molecular weights (PEG 300, 400 or 4000), dose-dependently reduced the gastric mucosal blood flow and volume of gastric secretion; these effects were greater in rats given PEG by the i.p. route, which also lowered acid output. Topical application of 1.5 mL absolute ethanol produced severe gastric mucosal injury, which was exacerbated by PEG; this lesion-aggravating effect was higher in the i.p.-injected groups. These findings indicate that when PEG is given by injection, it can adversely affect gastric function and increase the damaging action of alcohol. It is suggested that the use of PEG as a vehicle for injection should be re-assessed.