The analgesic dose-effect relationship of nefopam was compared in a double-blind randomised trial with that of oxycodone in immediate postoperative pain. Nefopam 15 mg or oxycodone 4 mg was given every 10 min i.v. (maximum six times) to patients in pain after upper abdominal surgery until their wound pain (scored 0-3) disappeared. The mean pain intensity (PI), initially 2.2 in both groups, descreased by approximately the same extent for up to two doses in both groups (to 1.5 after nefopam 30 mg and to 1.1 after oxycodone 8 mg). Thereafter PI was significantly less in the oxycodone group and diminished almost linearily to 0.1 after the sixth dose (24 mg). In the nefopam group, the PI score fell to 1.1 after the fourth dose (60 mg). This seemed to be the "ceiling" effect since additional doses up to 90 mg did not result in greater pain relief. In the oxycodone group, only two patients (12%) needed maximal dosage (6 x 4 mg), one of them requiring 32 mg of oxycodone. In the nefopam group, 12 patients (75%) needed further pain relief after the maximal dosage (6 x 15 mg). In these patients, oxycodone (maximally 16 mg) gave satisfactory analgesia. Drowsiness and a decrease in the respiratory rate were the principal side-effects of oxycodone, whereas tachycardia, restlessness, sweating and nausea were more frequent after nefopam.