N-Substituted N'-arylsulfony!oxamides display marked sugar-reducing activity and are relatively nontoxic [1-3]. We thought it relevant to structure--activity studies to examine the biological activ- ity of N-alkyl-N'-(2-amino-l,3,4-thiadiazol-5-ylsulfonyl)- and N-alkyl-N'-(5~sulfamoyl-l,3,4 - thiadiazol-2-yl)oxamides, in which the sulfonyl group is attached to a heterocycle. We synthesized these groups of compounds by the reactions ... N --J~ J",[----P4 H5OzOOOOO+~N-- ~ ...