The activities of cosmic‐ray‐produced radioisotopes P32, P33, and Be7, and of Pb210, which arises from the decay of radon, have been measured in samples of dust filtered from stratospheric and tropospheric air. The short‐lived activities appear to be in secular equilibrium with the respective local productions in various regions of the upper stratosphere. The activities of Pb210, on the other hand, are found to be uniform throughout the stratosphere. The implications of these and the tropospheric observations are discussed.

Cosmic‐ray‐induced activities have been detected in a few laboratory materials both at sea level and at mountain altitude. The measured amounts are found to be consistent with those expected to be produced from known flux of cosmic‐ray neutrons and negative muons.