Daily total ozone observations made with the Total Ozone Mapping Spectrometer (TOMS) flown on the satellite Nimbus-7 during 1978--1992, have been used in order to investigate the increase in the daily broad-band and spectral solar ultraviolet radiation reaching the ground through a recently developed parametric model. Total ozone reductions of 3.0% during summer time and 11% during winter time per decade, at St. Petersburg (60 ¿N, 30 ¿E), Russia, cause an increase in erythematically active ultraviolet irradiance of at least 7% and 22% respectively. ¿ American Geophysical Union 1995