D-region electron densities measured by rockets during the November 12, 1966, solar eclipse are shown to imply an effective recombination coefficient at an altitude of about 80 km of the order of 10−5 cm3 sec−1. The D-region electron densities between 65 and 83 km are computed for full-sun conditions assuming this value of recombination coefficient, the [37+] profile of Narcisi and Bailey [1965], and the NO profiles of Barth [1966], Pearce [1969], and Hesstvedt and Jansson [1969]. Electron densities between 60 and 65 km are estimated on the basis of the above-mentioned NO profiles and the negative-ion model of LeLevler and Branscomb [1968]. Also, electron densities between 80 and 90 km are computed by assuming an effective electron-ion recombination coefficient for NO+ and O2+ of 10−6 cm3 sec−1. There is a reasonable agreement between the computed electron densities and those measured by rockets launched from Wallops Island near 60° solar zenith angle. These results suggest that variability of D-region electron densities may be caused by changes in H2O vapor concentration induced by atmospheric circulation or eddy transport effects.