The high-resolution infrared bands centered at 769 and 1043 cm−1 for 1,2,4-triazine C3H3N3 have been analyzed, using the full asymmetric rotor Hamilton of Watson in A-reduced form using IIIr-representation. All the ground state rotation constants and three of the quartic centrifugal distortion constants could be determined with high precision from a simultaneous analysis of the two bands. The standard deviation of fit was 0.00077 cm−1. The upper state constants for the two bands have been determined with similar precision. The ground state rotational constants obtained from the present analysis are very similar to those predicted from theab initiostudy of the equilibrium structure. This strongly suggests that the similarity in several of the ring bond lengths, predicted in the latter, is indeed real.