The effects of iloprost, a synthetic carbacyclin derivative of prostacyclin (PGI 2) was studied in a standardized model of traumatic shock. Pentobarlitai anesthetized rats (33 mg/kg) subjected to Noble Collip drum trauma were characterized' by a 84 ± 10 minute survival time, a 16-fold increase in plasma cathepsin D activity, and a 5-fold increase in plasma myocardial depressant factor (MDF) activity. Iloprost significantly attenuated the accumulation of MDF activity in the plasma (69 ± 14 vs. 20 ± 6 U/ml) vehicle vs. drug (p<0.01), respectively, and significantly prolonged survival time to 243 ± 36 minutes (p<0.01). Plasma cathepsin D activity was also significantly attenuated (12 ± 1.8 vs. 6.2 ± 2.1 U/ml , vehicle vs. drug, respectively (p<0.02). Iloprost exhibited significant anti-proteolytic activity in pancreatic homogenates. Iloprost appears to exert a membrane stabilizing effect decreasing plasma cathepsin D activity and attentiating MDF production, probably secondarily to its anti-proteolytic effect and its maintenance of the splanchnic circulation. Iloprost may therefore prove to be a useful therapeutic agent in acute ischemic disorders including traumatic shock.