A new proton magnetic resonance (PMR) method for the quantitative determination of 2,5-Diaziridinyl-3,6-bis (carboethoxyamino)-1,4-benzoquinone and its acid decomposition products in dimethylsulfoxide-d6, and at 35 ± l° is described. The PMR spectrum of 2,5-Diaziridinyl-3,6-bis (carboethoxyamino) -1,4-benzoquinone shows singlet system at Δ 2.2 due to the protons of the two aziridine rings. The integral ratio of this signal to that of the methyl protons signal at Δ 1.2 and the methalene protons signal at Δ 4.05 is 4:3:2 in the intact molecule. The acid catalayzed decomposition results in disturbance of this ratio since the two aziridine rings are opened consecutively and a new multiplet signal appear at Δ 3.4–3.7 due to the ethelene group protons of the hydroxyethylamino group formed upon decomposition of aziridine moiety. Comparing the integral of the signal at Δ 1.2, 2.2, 3.4–3.7 and 4.03 to that of the sharp singlet at Δ 6.83 of 1,4 p-benzoquinone which is used as internal standard constitute the basis of the method.