An impairment of the survival of mice subjected to whole-body gamma-irradiation with a lethal dose of 10 Gy and treated with a repeated postirradiation administration of prostaglandin synthesis inhibitors (PGSls), indomcthacin or diclofenac, was observed. Morphological examination of the gastrointestinal tract and the estimation of blood loss into its lumen in animals treated with diclofenac did not show serious damage such as haemorrhages or perforation, but revealed structural injury to the intestinal mucosa indicating inflammatory processes. The lesions found arc supposed to be connected with increased intestinal permeability which leads to endotoxin escape from the gut and a subsequent increased mortality rate of irradiated animals. It may be concluded that PGSls are not suitable for the management of radiation sickness after an exposure to lethal doses of ionizing radiation