Observations with a four-channel UV radiometer in Santiago, Chile (33.5 ¿S, 70.6 ¿W) from January 1992 to December 1998 are presented. Channels are centered at 305, 320, 340 and 380 nm with a 10 nm bandwidth. Measurements were made at one-minute intervals. Hourly mean values at noon for 305 and 340 nm are presented as well as instantaneous irradiances for 60¿ of solar zenith angle. Their aperiodic variations on a seasonal scale are discussed with respect to the quasi-biennial oscillation (QBO) and ENSO phenomena. A significant positive trend that must be caused by decreasing total ozone is found in 305 nm irradiance. On a seasonal basis, this negative trend appears strong and significant during winter. ¿ 1999 American Geophysical Union