A new analgesic, nefopam, is chemically distinct and pharmacologically unrelated to any presently known analgesic. A comparison was made of morphine and nefopam in 74 patients who required parenteral analgesia for moderate to severe postoperative and somatic pain, using a single administration, 2-dose level, double-blind design. A significant dose-response curve was obtained with nefopam and with morphine, and there was no significant deviation from parallelism. The time-effect curves for the 2 drugs were similar. The estimated relative potency of nefopam to morphine indicates that 20 mg of neJopam HCI is the approximate analgesic equal of 12 mg of morphine SO4. There were no adverse effects with nefopam and one adverse reaction to morphine.