Sulfate ion was measured on air filtration samples obtained between 14 and 37 km at 33 ¿N. One concentration profile was determined each season in 1976. An average maximum mixing ratio of 1.4 ppbm was observed at 19 km. Sulfate was also observed on the filters exposed at the higher altitudes. The values at 24 km and above were quite variable, with an average value of 0.6 ppbm. ¿ 1977 American Geophysical Union