Balloon-borne particle counter measurements at Laramie, Wyoming (41 ¿N) are used to calculate the expected lidar backscatter at 0.694 μm wavelength from July 1979 to February 1982, a period which included at least four detectable perturbations of the stratospheric aerosol layer due to volcanic eruptions. These calculations are compared with lidar measurements conducted at Garmisch-Partenkirchen (47.5 ¿N) during the same period. While the agreement is generally good using only the main mode in the particle size distribution (radius ~0.07 μm) during approximately the first 6 months following a major volcanic eruption, a measured secondary mode near 1 μm radius, when included, improves the agreement. Calculations of the expected backscatter at 25--30 km reveal that substantial number of particles diffuse into this high altitude region about 7 months after a major eruption, and these particles should be taken into account when normalizing lidar at these altitudes.