The Angstr¿m coefficient profiles deduced from 93 SAGE Satellite observations in July 1980 between 50¿N and 70¿N have been used to study the variation of the aerosol size distribution in the Mount St. Helens aerosol layer. In most cases a layer of large particles corresponding to the maximum extinction at 18-20 km is topped by a layer of small particles. The study of profiles averaged over 10¿ latitude bands for May to November 1980 have confirmed the extent of this situation, which contrasts with a rather constant size distribution within the unperturbed stratosphere in 1979. Assuming an equivalent log-normal size distribution with an effective variance of 0.250, the logarithmic mode radius is found around 0.20 μm for the large-particle layer and around 0.06 μm for the top layer. The inferred mass density profile is strongly influenced by this structure.