Data from the backscattered ultraviolet instrument (BUV) on Nimbus 4 show depletion of ozone following solar proton events in January and September 1971 and in August 1972. The direct effect of high energy protons on the BUV instrument was determined by comparing nighttime BUV counting rates with particle data from IMP 6. The instrumental effects were then subtracted to allow accurate calculation of ozone profiles during the three events. The solar proton event of August 1972 was very large and produced an ozone depletion of 15% at 42 km that persisted for almost 30 days. This long recovery time indicates that NOx was produced in a quantity sufficient to alter the ozone chemistry. The two proton events in 1971 were of moderate size but produced ozone depletions of 10–30% at 50 km with a 36-hour recovery time. The rapid recovery is consistent with the assumption that HOx was responsible for altering the ozone chemistry, but the magnitude of the observed depletion exceeds that predicted by our chemical models.