The effects of a prostaglandin synthesis inhibitor (diclofenac, Voltaren) and an opiate (oxycodone, Oxanest) on postoperative pain were compared. Included in the study were 85 candidates for various operations. Patients requesting an analgesic were given either 75 mg of diclofenac or 10 mg of oxycodone as an intramuscular injection. The onset of analgesic effect occurred within 13 +/- 4 min with oxycodone and within 16 +/- 8 min with diclofenac. The analgesic effect of diclofenac was slightly weaker than that of oxycodone (on a pain scale of 1-4, 1.6/2.1 after 0.5 h and 1.5/1.8 after 1 h). The patients again asked for an analgesic after an average of 4.6 h in the oxycodone group and after an average of 6.1 h in the diclofenac group. The average number of injections required until the first postoperative morning was 2.5 in the oxycodone group and 1.8 in the diclofenac group. Side-effects: 21 patients in the oxycodone group reported a total of 39 side-effects and eight patients in the diclofenac group a total of 10 side-effects. Diclofenac is an alternative to opiates in the management of postoperative pain. It is especially useful in patients in whom opiates cause side-effects.