Syntheses are described for several 4-(1',2',4'-triazol-3'yl)pyridines, 3-and 4-(1',3',4'-thiadiazol-2'-yl)-pyridines, 3- and 4-(1',3',4'-oxadiazol-2'-yl)pyridines, 5-(1',3',4'-thiadiazol-2'-yl)pyrimidines and 5-(1',3',4'-oxadiazol-2'-yl)pyrimidines, all provided with a β-dimethylaminoethylthio side chain at the 5-position of the five-membered ring. The activities of these compounds as amplifiers of phleomycin-G against an in vitro culture of Escherichia coli B are tabulated and discussed.