In a double-blind, randomised and parallel clinical trial, two oral doses of dipyrone (1 and 2 g) administered every 8 h were compared with 10 mg of oral morphine given every 4 h for the relief of chronic cancer pain. A total of 121 patients with cancer pain without gastric involvement participated in a 7-day treatment course and were allocated to receive either dipyrone 1 g (n = 41), dipyrone 2 g (n = 38) or morphine (n = 42). Drug efficacy was analysed according to the degree of pain relief using a 100-mm visual analogue scale, and the number of patients who decided to increase the dose of the analgesic drug on day 4. The analgesic effect of dipyrone, 2 g every 8 h, was similar to that of morphine. The efficacy of both schedules was significantly greater than that of dipyrone, 1 g every 8 h. Dipyrone at either 1 or 2 g doses tended to be better tolerated than morphine, although the differences were not statistically significant.