A series of mono- and bis -(5'-substituted 1',3',4'-thiadiazol-2'- yl )pyridines with strongly basic side chains, e.g., 3,5-bis[5'(2'-N,N- dimethylaminoethylthio )-1',3',4'-thiadiazol-2'-yl]pyridine (1), and (5?-substituted 1',3',4'-thiadiazol-2'-ylmethyl)pyridines have been prepared for evaluation as amplifiers of phleomycin. Five of the six bis (5'-substituted 1',3',4'-thiadiazol-2'-yl)pyridines were themselves antibacterial under the test conditions, but compound (1) and the mono(5'-substituted 1',3',4'-thiadiazol-2'-yl)-pyridines and -methylpyridines displayed moderate two-to-three-star activity.