BACKGROUND: Residual muscle paralysis after anesthesia is reduced with the advent of intermediate-acting neuromuscular blocking drugs, yet the incidence is as high as about 10 percent. Opioids in patient-controlled analgesia (PCA) may cause respiratory depression and other problems after anesthesia. The purpose of this study is to evaluate the influence of PCA on the SPO₂, TOF ratio, head-lift and tongue protrusion during recovery room stay following intraoperative muscle relaxants. METHODS: 120 patients aged from 20 to 65 in ASA class I and II were divided into control or PCA groups. All patients received rocuronium (0.9 mg/kg) or atracurium (0.5 mg/kg) for tracheal intubation, and maintenance of relaxation was done with atracurium 0.2 mg/kg/hr during inhalation anesthesia. Reversal of block was done with pyridostigmine 0.15 mg/kg and glycopyrrolate 0.2 mg. SpO₂, TOF ratio, 5 sec-head lift, tongue protrusion tests were evaluated in the recovery room. RESULTS: IV-PCA did not influence the incidence of residual block, SPO₂, TOF ratio during recovery room stay for 20 minutes, but influenced negatively 5 sec-head lift test, tongue protrusion test only immediately after arrival at the recovery room. CONCLUSIONS: Since IV-PCA decreased the ability to perform head-lift and tongue protrusion early postoperatively, it is recommended that patients with IV-PCA should be carefully managed against the risk of aspiration or upper respiratory obstruction during their early recovery room stay.