Nine adult American bullfrogs (Lithobates catesbeianus) were tagged with an internal radio transmitter and tracked during one year in the valley of the Grote Nete (Belgium). The mean +/- SD core range area (KDE50) was 15.00 +/- 22.41m(2). The home range area (KDE95) had a mean +/- SD of 429.78 +/- 510.97m(2). Shores of larger eutrophic ponds and small temporary pools in alluvial forest were chosen as habitat. The total area used (MCP95) had a mean of 11,086.73 +/- 12,239.00m(2). The study revealed a mean action radius of 270.78 +/- 199.17m and individuals moved up to 742m in a single displacement. These results show that the dispersion of the American bullfrog in a valley system such as the Grote Nete can proceed very rapidly. A positive correlation between weight and distance covered within one movement was found, which could suggest that dominant individuals are capable of covering greater distances in search of optimal habitat for reproduction, foraging or hibernation. ; This study was financed by the EU Interreg IV A project IVA-VLANED-2.31 "Invasieve exoten in Vlaanderen en Zuid-Nederland-INVEXO" and the PWO-project "EXOUT" of University College PXL.