The Princeton University telescope on the Orbiting Astronomical Observatory 3 was used for occultation measurements of upper atmospheric species. The target star, &bgr; Cen, and observing date, July 26, 1975, were selected so that the line of sight grazed the earth's limb at local midnight. Observations at 2580, 2825, 2997, 3100, and 3428 ¿ produced ozone absorption data of high statistical accuracy between 48-km and 114-km tangent altitude. Near-exponential density profiles are obtained up to 85 km. Near 100 km a significant density excess above the extrapolated low-altitude profile is observed. Near-equatorial observations at altitudes up to approximately 75 km agree well with theoretical calculations. Ozone densities measured at 6.5¿--12.5 ¿S above approximately 75 km exceed our theoretical calcultions and are not understood at the present time. A search for the 1188-¿ chlorine line in the 1187-¿ O2 absorption feature was carried out at tangent altitudes of 96--116 km. An upper limit to the atomic chlorine mixing ratio at 106 km of 3 ppb is found. This upper limit exceeds the expected value for atomic chlorine by a factor of approximately 2.5.