A procedure for quantitative determination of 5-methyl- 6-nitro-7-oxo-1,2,4-triazolo[1,5-a]pirimidinide l -argininy was developed using the HPLC method with UV detection. To achieve the best chromatographic characteristics, it is proposed to use a column with a grafted octadecylsilyl phase 5-100-c18 (EKA, Sweden). The possibility of applying the developed procedure for the technological control of the third stage of the drug «Triazid» preparation was proved by the validation.