The effect of (CO)-C-60 gamma-radiation on the individual bicyclic dienes 5-vinyl-2-norbornene (VNB) and 5-ethylidene-2-norbornene (ENB) and dilute (0.01-1.0 mol/l) solutions of VNB in heptane, cyclohexane, and benzene was studied. Chain polymerization processes occur in gamma-irradiated individual dienes, as indicated by the high initial radiation-chemical yield of diene conversion: G(0)(-VNB) = 640 mol/100 eV and G(0)(-ENB) = 360 mol/100 eV. At doses higher than 14 Mrad (1 rad = 0.01 Gy), polymer formation processes are accompanied by the reverse processes of depolymerization, which result (in the range of 14-100 Mrad) in the appearance of a plateau (at a polymer content of 14.5%) on the dose dependence of VNB conversion and in a 90-fold decrease in the rate of ENB consumption as compared to the initial (0-14 Mrad) region. It was found that the G(0)(-VNB) values fall on a straight line G(0)(-VNB) = 620C(0)(VNB) in the concentration plots for VNB solutions in heptane and cyclohexane and on another straight line Go(-VNB) = 180C(0)(VNB) for VNB solutions in benzene. These findings are explained in terms of the indirect ionization of VNB molecules in heptane and cyclohexane, since the first ionization potentials equal for the solvents (heptane and cyclohexane) are higher than the ionization potential of VNB, and the involvement of excited benzene molecules in VNB decay processes.