A calorimetric method associated with a Co-60 source has been devised for the determination of vinyl monomer c_p values in the presence of inhibitors to prevent polymerization. The heat source is the same interaction of the $\gamma$ rays in the bulk of the monomer and the increase in temperature has been determined by the use of a thermistor in adiabatic conditions. The advantage of the method consists in the fact that the measurements can be made over a large range of temperatures. The results obtained are in good agreement with the data in the literature.