The second-order multireference Møller–Plesset perturbation method (MRMP) was applied to the accurate estimation of the transition state barrier height of H2CO→H2+CO reaction. The best estimate for the classical barrier height is 84.5 kcal/mol at the highest level of MRMP theory with the quadruple zeta plus triple polarization basis set and with the active space of 12 electrons in 11 active orbitals. The inclusion of zero-point vibrational energy correction reduces the activation energy to 79.1 kcal/mol, which is in excellent agreement with the experimental value of 79.2±0.8 kcal/mol [Polik, Guyer, and Moore, J. Chem. Phys. 92, 3453 (1990)]. Analysis of the second-order energies in terms of internal, semi-internal, and external contributions shows that the present MRMP provides a well balanced treatment for the estimation of the energy difference between the equilibrium and transition state structures. © 1997 American Institute of Physics.