Solutions of 5-vinyl-2-norbornene (VNB, 5-vinylbicyclo[2.2.1]hept-2-ene) and the related compounds 5-ethylidene-2-norbornene (ENB, 5-ethylidenbicyclo[2.2.1]hept-2-ene) and 2-vinyl-2-norbornane (VNN, 2-vinylbicyclo[2.2.1]heptane) in cyclohexane have been irradiated with gamma-rays at 40A degrees C. The initial radiation-chemical yields G (0) for the consumption of the solutes and the formation of final products of gamma-radiolysis of the solvent cyclohexane have been determined. It has been shown that solute consumption and molecular hydrogen formation yields G (0)(-RH) and G (0)(H-2), respectively, are linearly related to the first vertical ionization potential of the solute. The G (0) values of molecular hydrogen, cyclopentadiene (CPD), butadiene, and methylallene, minor products of gamma-radiolysis (40A degrees C) of liquid VNB, ENB, and dicyclopentadiene (tricyclo[5.2.1.0(2.6)]decadiene-3.8), have been determined. It has been shown that the G (0) values of CPD formation linearly depend on the first vertical ionization potentials of gamma-irradiated bicyclic dienes. It is concluded that the gamma-irradiation of cyclohexane generates two kinds of radical cations, which differ in mobility and reactivity.