On the basis of the results of an earlier study, showing that i.v. indoprofen induced no clinically significant changes in hemodynamic parameters of patients with acute myocardial infarction (AMI), a double-blind randomized trial was carried out in 40 AMI patients to evaluate the analgesic activity of 400 mg i.v. indoprofen in comparison with 10 mg i.m. morphine hydrochloride. Pain severity was recorded before and at several intervals within 24 h after drug administration. The average analgesic response was prompt and progressive up to the 6th hour in both treatment groups, with no significant difference between drugs in various pain descriptors. However, the proportion of responding patients in indoprofen group was greater than in morphine group at all observation times, indicating a significant difference (p less than 0.05) in favor of indoprofen. In view of its good tolerability, i.v. indoprofen is worth considering in early AMI as an alternative to morphine in those patients in whom non-opiate analgesia might be preferable.