The electron microscope has been used to observe the behavior of He gas bubbles in neutron irradiated Al-Li alloys. In the case of high He concentration, the gas bubbles were observed as small white or black dots in specimens as irradiated. The bubbles initiated appreciable growth upon heating to 400°C. They precipitated preferentially along the subgrain boundaries and dislocations, as well as along the grain boundaries. The size of the bubbles, observed in a specimen heated to 550°C, ranged from about 10 Å to 1 μ. The shape of the bubbles in the specimen heated to 400°C was hexagonal or octagonal in the two-dimentional projection and a polyhedral image of the larger bubbles was clearly observed. The number of planes that bound the polyhedral bubble increased with increasing temperature of heating. Spherical bubbles were also observed.