Sixty unpremedicated patients presenting for day-care arthroscopy surgery were allocated randomly to receive diclofenac 1 mg kg-1 i.m., fentanyl 1 microgram kg-1 i.v. or no analgesic during the course of anaesthesia. Patients receiving fentanyl had slightly, although not significantly prolonged recovery times. Patients receiving diclofenac had significantly improved postoperative visual analogue pain scores compared with patients receiving placebo medication (P less than 0.05). With fentanyl, pain scores were reduced also, but the effect was not statistically significant. Both fentanyl and diclofenac produced significant reduction in postoperative analgesic requirements (P less than 0.05). We conclude that diclofenac 1 mg kg-1 i.m. was an effective analgesic for arthroscopic procedures on the knee and is a useful alternative to opioids for day-care patients.