Stratospheric temperatures at high latitudes in the 10- to 30-mbar layer are found to have been approximately in phase with the solar cycle during the period 1951--1970. These findings suggest an influence by galactic or solar cosmic rays. To study the possible effect of solar proton events on stratospheric temperatures, we have chosen to investigate one of the largest known solar proton events, that of August 1972. It is expected that after this event, significant changes in the temperature and ozone distributions should have taken place at high latitudes. This is tentatively confirmed by experimental data from the Canadian stations. It is tentatively proposed that variations in stratospheric temperatures and ozone concentrations at high latitudes over the solar cycle may be caused by similar variations in the production rates of nitric oxide by galactic or solar cosmic rays or a combination of both.