The results of rocket measurements of ozone and nitric oxide concentrations, vertical component of the electric field strength, positive ion density, and temperature of the middle atmosphere during the extremely strong solar proton events (SPE) of October 1989 are presented. The measurements were taken in the southern hemisphere in the Indian Ocean (40¿--60¿S and 45¿--75¿E) on board the research vessel Akademik Shirshov. A great increase in ion densities above ~30 km and nitric oxide concentrations above ~40 km with maximum ~2¿109 cm-3 at ~45- to 55-km heights were observed during the SPE. A decrease in ozone concentrations above ~35 km with the maximum decrease of about 20--25% at ~50-km height and cooling of the atmosphere at ~40- to 60-km heights with the maximum temperature decrease of about 14¿K near 50 km were also observed. An unexpectedly large value of the vertical electric field strength of 12 V/m was detected in the lower mesosphere at about 58 km at 58¿30'S during the SPE. The obtained results on ozone, nitric oxide, ion concentration, and temperature qualitatively agree with the existing photochemical concepts on the impact of solar proton events on the middle atmosphere, while the measured cooling of the stratopause is greater than that predicted by theoretical models. The increase of the vertical electric field strength observed during the SPE points out a very high electrical activity of the mesosphere and unknown generation mechanisms of electrical phenomena in the middle atmosphere. ¿ American Geophysical Union 1994