In view of the part played by renal prostaglandins in the mechanisms responsible for pain in renal colic, it was worth trying to find out whether nonsteroidal anti-inflammatory agents, which inhibit prostaglandin synthesis, have an analgesic effect of their own. In a double-blind trial the effects of ketoprofen 100 mg administered intravenously alone or associated with noramidopyrine were investigated in 62 patients divided at random into two equal groups. A rapid analgesic effect was observed with no significant difference between the groups. No severe side-effects were recorded. The double-blind method made it possible to confirm that ketoprofen administered alone relieved pain in 97% of the patients (with complete sedation in 45%) and acted within 5 minutes. Owing to their effectiveness and safety nonsteroidal anti-inflammatory drugs (especially ketoprofen) may be proposed as an alternative to conventional treatments of renal colic. But because of their activity they should not be prescribed until a firm diagnosis has been made. The cause of the colic should also be rapidly determined in order to treat it as well as the pain it produces.