The antisymmetric amino wagging vibrational state of hydrazine in the 10 μm region was investigated by infrared–microwave double resonance. Nearly 200 microwave transitions were measured in the frequency range of 6–60 GHz using N2O and isotopic CO2 lasers. Among the microwave transitions 27 were assigned as those of the ground vibrational state and nine as those of the vibrationally excited state. About 20 infrared absorption lines were assigned based on the double resonance measurements. The excited state rotational constants, the internal rotation splittings, the inversion splittings, the Coriolis splittings, and the band origin were determined accurately.