A series of [(3-aryl-1,2-benzisoxazol-6-yl)oxy]acetic acids was synthesized and tested for diuretic activity in saline-loaded mice and in conscious, water-loaded dogs. The structural requirements for good diuretic activity in both mice and dogs were found to be very specific. In summary, the compounds with the best diuretic activity (13i, 13q, and 13ff) were substituted with a 2-fluorophenyl group at the 3 position and chlorine or bromine at the 7 position. Compound 13ff, [(7-bromo-3-(2-fluorophenyl)-1,2-benzisoxazol-6-yl]oxy]acetic acid (HP 522), was found to be moderately uricosuric in chimpanzees and was selected for further development.