Lasers in the triplet spectroscopic series of molecular hydrogen and molecular deuterium were discovered in the mid-infrared band. These are at 3.84, 3.77 and 3.71 microns in ydrogen and at 4.71, 4.60 and 4.52 microns in deuterium. These lasers operate in the a3 - On system in both molecules but the assignment is not so certain in deuterium Ã‚Â§s it is in hydrogen because of the lack of sufficient spectroscopic coefficients for the c3 state. The laser data have been used to identify heretofore unidentified infrared lines in hydrogen and deuterium. Future work is planned to include extension of the laser data base for the AV = -1 transitions and an attempt to produce the AV = 0 lasers.