An analysis of measured solar radiation data in Trabzon (lat, 41 degrees 10'N, long. 40 degrees 20'E, placed on the Black Sea side) is presented in the form of hourly-average, monthly-average daily and percentage frequency distribution. The experimental data corresponds to the period from Jan. 1990 to Dec. 1993. Applying the measured data, correlation models for calculating the hourly and monthly diffuse radiations are derived. (C) 1998 Elsevier Science Ltd. All rights reserved.