An analysis of the ultraviolet radiation measurements taken at Belsk by Robertson-Berger meter and Brewer spectrophotometer over the period 1976--1997 is performed. In the Robertson-Berger data series, a mean level shift that can be attributed to change in calibration procedure was detected. In the examination of the series, a wavelet analysis was used. To determine the magnitude of the shift, a relationship between UV radiation and total ozone for a clear sky was applied. The results showed that for the Robertson-Berger data, over the period 1984--1992, the correction factor of 1.14 should be applied. The trend in the whole observational period was 6.1¿2.9% per decade. In the estimation of the trend uncertainty, the autocorrelation in the noise and shift of the level in the data was taken into account. The UV-B trend depends mainly on the trend of ozone, and the response of UV-B to ozone changes is most evident for the variations of the ozone content at a large timescale. ¿ 2000 American Geophysical Union