Microwave spectra of (H3N)-N-14-(HNO3)-N-14. (H3N)-N-15-(HNO3)-N-14, (H3N)-N-14-(HNO3)-N-15, and (H3N)-N-14-(DNO3)-N-14 have been obtained by Fourier transform spectroscopy in a supersonic jet. The spectra are consistent with a hydrogen-bonded structure having a planar arrangement of the heavy atom frame and a linear or near-linear hydrogen bond involving the HNO3 proton and the lone pair on the ammonia. The hydrogen bond length obtained from the rotational constants is 1.736(63) Angstrom and the nitrogen-nitrogen separation is 3.344(12) Angstrom. The NO single bond of the nitric acid and the C-3 axis of the NH3 form angles of 54(4)degrees and 21(3)degrees, respectively, with the line joining the centers of mass of the monomers. The hydrogen bond length is significantly shorter than that observed in related complexes such as H3N-HCl and H3N-HBr, indicating a particularly strong interaction between ammonia and nitric acid.