A series of 6,11-dihydro-11-oxodibenz[b,e]oxepinacetic acids was synthesized and the antiinflammatory activity determined. Studies on 29 compounds revealed certain structure-activity relationships. In the carrageenan edema test, eight compounds exhibited higher antiinflammatory activities than did indomethacin. Several compounds (2, 9, 14, 22, 25) also proved to have activities superior or comparable to indomethacin in suppressing chronic as well as acute inflammation and carrageenan-induced hyperesthesia. Gastric irritation and lethality rates were less frequently observed with these compounds.