This paper analyses hourly data of global ultraviolet (290-385nm) and global irradiation over a horizontal surface. The data was taken in Valencia (39.5degreesN, 0.341W) and Cordoba (37.51degreesN, 4degrees48W), (Spain) during the years 1996-1999. In order to estimate the ultraviolet solar radiation using global solar radiation values over a horizontal surface, the method of Foyo-Moreno et al. (Foyo-Moreno, I., J. Vida and L. Alados-Arboleda. J. Appl. Meteor. 1998, 38, 1020-1026) has been used. The results obtained with this method are satisfactory with a determination ratio r(2) = 0.98, RMSE = 9.3%, MBE = 0.5% for Valencia and r(2) = 0.99, RMSE = 6.2%, MBE = 0.3% for Cordoba. (C) 2002 Published by Elsevier Science Ltd.