ABSTRACTA series of new 4,5-dihydro-6-oxo-1,2,4-triazino[4,5-b]1,2,3,4-tetrahydro-β-carbolines were synthesized by the reaction of methyl 1,2,3,4-tetrahydro-β-carboline-3-carboxylate and the appropriate hydrazonoyl halide in presence of triethylamine. The structures of the title compounds have been established by their elemental analyses and spectroscopecal data. The microbial features of some of the synthesized compounds were studiedby a known method.