Physicochemical parameters, natural radioactivity and heavy metals on the surface waters of rivers in Epirus (Aoos, Kalamas, Louros), Macedonia (Aliakmonas) and Thessalia (Pinios) were measured during the period May 2004-May 2006 in three sampling sites of each river. All the determined metal concentration values were lower than the ones usually found in polluted areas while each individual element displayed a wide variation in its concentration. Gross-alpha and -beta activities in the five Greek rivers were within the range usually observed in other European and world rivers. All Ra-266 concentrations were lower than the world mean of 0.015 Bq L-1. Statistical analysis of variance and correlation analysis of the measured metals showed limited significant differences between sampling sites or periods, suggesting influence from geologic factors rather than from point sources. Significant differences between the three studied sites of Aliakmonas river were observed for gross-alpha and Ra-266 activities and this result was attributed to the influence of the coal mines in the region and/or the runoff of fertilizers from agricultural activities in this area.