Recent laboratory measurements of the molecular oxygen photoabsorption cross section at a temperature of 195 K provide a more suitable basis for the determination of mesospheric molecular oxygen densities than previously available room temperature cross sections. The 195 K cross sections have been used to analyze the data from 34 rocket measurements of the atmospheric extinction of solar Lyman &agr; radiation. Observations from Woomera (31¿S) are compared with those from other locations (mainly 35¿ and 59 ¿N), and separate mean molecular oxygen density profiles are derived for each of the three latitudinal groups. Averaging the data from the flights at all locations yields an observational mean molecular oxygen density profile which exceeds the mean Cira (1972) model by about 20% at 70 km and by about 9% at 90 km. Part of this difference may be due to residual effects on the cross section of temperature variatons in the 70- to 90-km region. Absorbers other than molecular oxygen probably account for a major part of the remaining difference between the observations and the model, and further refinement of the Lyman &agr; extinction technique will require a more accurate estimate of these corrections.