The air sensitivity of C60 intercalated with an alkali metal has been known for some years. It is shown here that for K6C60 and Rb6C60 the route by which the deintercalation occurs involves-rather unexpectedly-the formation of the alkali metal carbonates, not the oxides. This observation is used to explain why impurity oxygen does not exist in alkali-metal-intercalated C60 although it is extremely difficult to remove oxygen from non-intercalated C60.