Previous studies have suggested that methylprednisolone (MP) pretreatment attenuates the usual hemodynamic response to naloxone (NAL) treatment of hypovolemic shock. In this study, both drugs were given concurrently during shock to evaluate hemodynamic changes, plasma endorphin-like activity (PELA), and survival. Twenty-six dogs were bled to a mean arterial pressure (MAP) of 40 to 45 mm Hg, which was maintained for 45 min. Animals were then treated with iv 0.9% NaCl (NS), 5 ml; NAL, 4 mg/kg; MP, 30 mg/kg; or NAL, 4 mg/kg, plus MP, 30 mg/kg. Animals treated with NAL and/or MP had significantly (p < .05) improved MAP, cardiac output, and myocardial contractility compared with NS-treated animals. NAL and MP each significantly lowered PELA levels and both NAL and NAL plus MP significantly improved survival.