Etodolac, 1,8-diethyl-1,3,4,9-tetrahydropyrano[3,4-b]indole-1-acetic acid, a clinically effective analgesic and antiinflammatory agent, has been resolved via a chromatographic separation of its diastereoisomeric esters with (-)-borneol. The effects of the enantiomers were studied in vitro on prostaglandin synthetase and on adjuvant-induced arthritis in rats. The biochemical and pharmacological results show that virtually all of the effects of etodolac are due to the (+) enantiomer.