Thioethers, appropriate for testing as amplifiers of phleomycin against in vitro cultures of Escherichia coli, are prepared via corresponding thiones in the purine, imidazo[4,5-b(and 4,5-c)]pyridine, pyrazolo[3,4-d]pyrimidine, quinazoline, benzothiazole, benzoxazole, pyrimidine, imidazole, thiazoline, 1,2,4-triazole, s-triazolo[4,3-c(and 1,5-c)]pyrimidine, oxazolo[4,5-b]pyridine, quinoline and 1,3,5-triazine series. Structures are confirmed by N.M.R. spectra. Biological activities are tabulated and discussed in terms of structure.