To evaluate the efficacy of opiate administration regimens, 32 patients with multiple rib fractures were prospectively randomized to receive either continuous epidural (ED) or continuous intravenous (IV) infusions of fentanyl. Dosage was titrated to individual subjective pain relief. Ventilatory function tests (VFTs), arterial blood gases (ABGs), and visual analog scores were obtained before and after the institution of analgesia. Post-analgesia values were compared with pre-analgesia values using a two-tailed paired t-test looking for significant changes produced by the analgesic method. Both methods significantly improved analog pain scores. The ED method produced improvement in both maximum inspiratory pressure (MIP) and vital capacity (VC), whereas IV analgesia only produced improvement in VC. Intravenous fentanyl produced increases in PaCO2 and decreases in PaO2, whereas no significant changes in ABGs were observed with ED fentanyl administration. Side effects were similar between the groups, with pruritus being more pronounced with ED fentanyl administration. The data demonstrate that the continuous ED fentanyl method offers excellent relief of pain and improvement in ventilatory function and has distinct advantages over IV fentanyl administration with respect to changes in ABGs and MIP. The continuous infusion of epidural opiates should be the preferred analgesic method for patients at high risk of developing pulmonary complications following multiple rib fractures.