BIOSIS COPYRIGHT: BIOL ABS. The concentration of 14 heavy metals in the tissues of the frog Rana ridibunda, living in a small river of Macedonia, Northern Greece. was investigated. The liver contained significantly higher amounts of copper (1041|153 mg/kg dry wt), cobalt (6 | 0.1 mg/kg), molybdenum (22 | 7 mg/kg), chromium (41|11 mg/kg), and cadmium (2 | 0.2 mg/kg), while the carcass contained significantly higher amounts of aluminum (303 | 67 mg/kg), manganese (164|38 mg/kg), nickel (27 | 3 mg/kg), strontium (419 | 34 mg/kg), and barium (93.1|1 mg/kg). High concentrations of copper, chromium, molybdenum, zinc, manganese, and aluminum, corresponding to the highly polluted areas, were detected. For some other metals, such as cobalt, nickel, lead, cadmium, and cesium, the river could be classified as moderately to heavily polluted. The main sources of the river pollution seem to be fertilizers containing heavy metals as trace elements, pesticides with a heavy metal in their formula, urban runoff, a