A series of pyrazinethiols and pyrimidinethiols with phenyl substituents have been prepared and converted into their carbamoylmethylthio, 2-dimethylaminoethylthio and 2-aminoethylthio derivatives. Similar derivatives of pyrazine-2,3- and -2,6-dithiol were also prepared together with N,N-dimethyl-2-(1′- and 2′- naphthyloxy)ethylamine. As amplifiers of phleomycin these compounds showed moderate two-to- three-star activity.