The first mass-analyzed threshold ionization (MATI) spectra from molecular excited triplet states have been collected for benzene and perdeuteriobenzene from the B-3(1u), lowest triplet state. From these spectra, the C6H6 B-3(1u) state energy is found to be 29 627 +/- 12 cm(-1) and the C6D6 B-3(1u) state energy is found to be 29 828 +/- 12 cm(-1). The MATI spectrum for each species was collected from 1000 cm(-1) below the ionization threshold to similar to2000 cm(-1) above the threshold. Hot band structure allowed for the first higher-resolution gas phase vibrational measurement of the nu(1), nu(8), and nu(6) frequencies in the B-3(1u) state. They were found at 927, 229, and 575 cm(-1) for the protonated molecule and at 832, 200, and 528 cm(-1) for the deuterated molecule, respectively. New vibrational structure has also been observed in the cation ground state of both molecules.