Characteristic features of the molecular geometry and electron density distribution in the crystals of 3,6-dimethoxy-1,2,4,5-tetrazine and 3-phenyl-1,2,4,5-tetrazine have been studied by X-ray structural analysis and quantum-chemical (RHF and MP2) and molecular mechanics (MM3) calculations. An unusual shift of the maxima of the deformation electron density from the N-N bonds toward the center of the heterocycles was found, which may be interpreted as a ''bending'' of the corresponding bonds. This ''bending'' was confirmed by calculations of characteristics of the electron density distribution within the multipole model.