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4,6-Disubstituted 2-(morpholinocarbonyl)furo[3,2-b]indole derivatives showed analgesic and antiinflammatory activities when assayed by the acetic acid writhing test in mice and the carrageenin edema test in rats. To understand how the substituents affect the biological activities, the quantitative structure-activity relationships (QSAR) of 38 compounds were analyzed using the adaptive least-squares method (ALS method). The resulting QSAR suggested that some chemical modifications of 4,6-disubstituted furo[3,2-b]indole derivatives would improve their biological activities. Thus, 15 additional compounds were synthesized to reinforce and confirm the correlation. Among these compounds, particularly 4-(2-ethylhexanoyl)-2-(morpholinocarbonyl)-6-(trifluoromethy l) furo[3,2-b]indole showed pronounced biological activities. This compound gave a pharmacological activity spectrum similar to that of tiaramide but exhibited much higher potency.