The vibronic (vibrational-electronic) interactions in the pi-anion radicals of the metalloporphyrins (MCr, Mn, Fe, Co, Ni, Cu, and Zn), which show delocalized D-4h structures in the neutral states, are discussed using B3LYP density-functional-theory calculations. The B-1g and B-2g modes of vibration can remove the degenerate E-2(g) state of the pi-anion radicals in the D-4h symmetric structures to lead to rectangular and diamond D-2h distortions, respectively. Calculated vibronic coupling constants demonstrate that the B-1g modes of vibration better couple with the degenerate electronic state, leading to the rectangular D-2h distortion. In particular, the B-1g modes of nu(10) and nu(11), which have dominant contributions from C-alpha-C-m and C-beta-C-beta stretching, give large vibronic coupling constants in the pi-anion radicals. The vibronic coupling constant can be viewed as the Jahn-Teller distortion force, and therefore these C-C stretching B-1g modes will play a central role in the Jahn-Teller effect of the pi-anion radicals of the metalloporphyrins.