It is shown that the Drell-Hearn sum rule can be obtained from the equal-time commutator $\left[D^{+}\mathrm{}\right(t),D^{-}\mathrm{}(t\left)\right]=0, \mathrm{where} D^{\pm }\mathrm{}\left(t\right)=\int d^{3}x\frac{x_1\pm i{x}_2}{\sqrt{2}}\rho \mathrm{}\left(x\right)\mathrm{},$ $\rho \mathrm{}\left(x\right)\mathrm{}$ being the electric charge density.

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