2-(2-Isopropyl-5-indanyl)propionic acid (UP 517-03) is a new anti-inflammatory agent with marked analgesic and antipyretic properties. The anti-inflammatory potency is greater than that of phenylbutazone but lower than that of indometacin. This effect is observed also in adrenalectomized rats. The analgesic activity in the Randall and Selitto test is equipotent to that of indometacin, but this potency is lower in the other tests. In lowering brewer's yeast-induced fever in rats, UP 517-03 is as potent as indometacin and 10 times more effective than phenylbutazone. Considering from pharmacological index, UP 517-03 is tolerated as well as phenylbutazone and better than indometacin.