On May 7, 1963, at 1611 EST an Aerobee Hi rocket was launched from Wallops Island, Virginia, carrying a filtered photometer that measured the intensity of the (O, O) negative band of N2+ in the dayglow from 100 to 223 km. The total zenith intensity at 3914 A was observed to decrease from 6.7 kR at 100 km to 5.4 kR at the peak altitude, indicating that the majority of excited N2+ ions was located above 223 km in the F2 region. Resonance scattering of sunlight by pre-existing N2+ ions appears to be the principal excitation mechanism for the first negative bands in the dayglow. Simultaneous ionization-excitation of nitrogen by solar EUV radiation apparently plays a minor role, and an upper limit is placed on its contribution to the intensity of the (0, 0) negative band. The experimental results are analyzed by assuming that photoionization is the principal source mechanism for N2+ in the daytime ionosphere and that dissociative recombination, charge transfer, and ion-atom interchange with the atmospheric gases are the chief loss processes. It is shown that dissociative recombination is a minor loss mechanism below 200 km and that N2+ ions are destroyed principally in reactions with O and O2 at these altitudes.