We report a new measurement for the cosmic ray sea level ionization, 2.15¿0.05 in ion pairs/s cm3, in agreement with the previous determination by Shamos and Liboff (1966) (2.18¿0.05 ion pairs/s cm3) and the calculation by O'Brien (1970) for solar minimum (2.22 ion pairs/s cm3). In contrast with the 1966 measurement (which used CCl2F2), the present work was done in an air-filled 906-1 aluminum chamber, with a wall thickness of ~0.3g/cm2. Measurements were conducted over Lake St. Clair and Lake Huron during 1973 and 1974. Corrections for alpha and beta wall contamination were made in two independent ways, by an analysis of the ion current fluctuations and by operating the chamber in the low-background Morton Salt Company Mine, located 600 m below ground in Painesville, Ohio.