The large depletions in column ozone observed over Antarctica during spring imply enhanced levels of solar ultraviolet radiation at the Earth's surface. Daily data from the Nimbus 7 Total Ozone Mapping Spectrometer were combined with a model of atmospheric radiative transfer to compute the time evolution of ultraviolet irradiance, at wavelengths from 290 to 350 nm, incident on McMurdo Station during September--October 1987. Large changes in column ozone occur as the polar vortex moves over the site. This is accompanied by correspondingly large variations in ultraviolet radiation at the Earth's surface. At a wavelength near 305 nm, the irradiance in early October exceeds values appropriate to an unperturbed ozone layer by a factor of 5--6. As December 21 approaches, the noontime ultraviolet irradiance increases, irrespective of changes in ozone. Any lengthening of the period of ozone depletion toward summer solstice will have a substantial impact on the ultraviolet irradiance received by the Antarctic surface. ¿ American Geophysical Union 1989