The invention relates to thiazolidine derivatives having in 4-position a hydroxy group and a 3'-sulphamyl-phenyl substituent the phenyl ring of which is di-substituted by halogen or methyl, in 2 position an imino group and in 1-position an aliphatic or cycloaliphatic substituent. Said thiazolidines have diuretic activity. The invention also relates to a process for the manufacture of said compounds.