Simulation data of second virial coefficients have been obtained for an off-lattice model of linear polymer chains by means of Monte Carlo method with different values of the variable that describes intramolecular attractions between units. The data have allowed us to study the theta, or tricritical, region where binary interactions cancel out. These Monte Carlo results are quantitatively compared with numerical predictions from the tricritical renormalization group theory. With this purpose, we have employed the same values for the three-body and the cutoff theoretical parameters that were previously used to reproduce the mean size data.