Absolute partial cross sections for electron-impact ionization of nitric oxide and nitrogen dioxide are reported for electron energies from threshold to 1000 eV. The product ions are mass analyzed using a time-of-flight mass spectrometer and detected with a position-sensitive detector whose output demonstrates that all product ions are collected irrespective of their initial kinetic energy. Data are presented for the production of NO+, N+, O+, and NO2+ ions from NO; and for the production of NO2+, NO+, N+, O+, and (N2++O2+) ions from NO2. The overall uncertainty in the absolute cross section values is +/- 5% for singly charged parent ions, while that for the fragment ions may be as large as +/- 20%. For NO, the previously published data are generally in reasonable agreement with those presented here, although there remain some significant discrepancies with even the most recent work. No previous comprehensive study of NO2 has apparently been reported but the experimental NO2+ cross section data that are available disagree substantially with the present measurements. The present total NO2 cross section is, however, in excellent agreement with recent theoretical work.