Absolute cross sections for emission of Lyman &agr; radiation have been determined for low-energy H and H+ impact on N2 and O2 targets. Data were obtained for projectile energies between about 0.04 and 2.5 keV. Using previously measured cross sections for Balmer &agr; and Balmer &bgr; emission, we were able to evaluate the cascade contributions to the measured Lyman &agr; signals and to deduce the cross sections for both direct 2p state excitation and total Lyman &agr; emission. The data are compared with other results for projectile energies below 10 keV, and the problems associated with the application of such cross-section data to proton auroral analyses are discussed. ¿ American Geophysical Union 1988