Profiles of sulfate mixing ration versus altitude over the range 15-28 km were obtained from filter sample collected aboard balloons and U-2 aircraft. Observations were made in the summer, fall, and winter following the March-April, 1982, El Chichon eruption. Observed sulfate mixing ratios were approximately two orders of magnitude greater than typical background (not volcanically augmented) mixing ratios. The sulfate mixing ratios obtained from the aircraft filter measurements were in good agreement with the results from a wire impactor and a particle counter flown simultaneously. Computations of the amount of sulfate contained in a vertical column of 1 m2 were in agreement with similar calculations from airborne lidar, balloon-borne particle counters, and Solar Mesosphere Explorer satellite radiance retrievals.