2, 3-Dihydrobenzofuran derivatives having various sulfamoyl groups at the 5-position were synthesized and tested for oral diuretic and saluretic activities in rats and mice. Intraperitoneal uricosuric activity was also tested by a clearance method using oxonate-treated rats. Structureactivity relationships are presented. The 6, 7-dichloro-5-N, N-disubstituted sulfamoyl-2, 3-dihydro-benzofuran-2-carboxylic acids (9ab, ac, 13a and b) having lower alkyl substituents showed the most potent diuretic and saluretic activities among the compounds synthesized. Hyperuricosuric activity was observed in 6, 7-dichloro-2, 3-dihydrobenzofuran-2-carboxylic acids and 2-hydroxymethyl-6, 7-dichloro-2, 3-dihydrobenzofurans having a 5-sulfamoyl group, with relatively small substituents (9aa-ac, af, ak, al, an, ao and 16a-c). The saluretic activity of 9ab showed a high-ceiling profile. Examination of the enantiomers of 9ab revealed that the (-) -enantiomer is responsible for most of the diuretic and saluretic activities, while the (+) -enantiomer is responsible for most of the uricosuric activity.