Records of the behaviour of aluminized grenade glow clouds at twilight and at night were obtained using cameras and photometers. From these records the radiance, radiant p~wer, and radiant energy have been deduced for the altitude range 100-200 km. The twilight observations show that the absorption cross section of aluminium monoxide is about 3 X lO-14 cm2? From the night-time results it is concluded that the glow probably arises from a chemiluminescent reaction with atomic oxygen. A set of reactions consistent with the observations above 120 km altitude is