Hourly and two-minute averages of ultraviolet (295-385 nm) and global radiation have been measured at Istanbul since January 1992. Monthly averages of hourly UV radiation varied from a minimum of 4.23 W/m(2) in December to a maximum of 29.76 W/m(2) in August at midday. UV radiation received on the ground at Istanbul did not increase from 1992 to 1994. Annual averages of the daily total UV for 1992, 1993, and 1994 are, respectively, 130.4, 110.8, and 110.0 Wh/m(2). The ratio of UV to global radiation averages 0.02-0.06 during the year and depends on cloud conditions.