To determine the gene flow of Chaoborus crystallinus, populations throughout Europe were sampled. To test if the gene flow is higher within regions than between regions and to investigate if regional populations may act as metapopulations, four regions with several populations each were examined. For a detailed analysis of the regional gene flow, subregions within one region were analysed. Allozymes and mitochondrial restriction fragment length polymorphism (RFLP) were used to estimate the relative amounts of gene flow. On the European scale gene flow between populations within regions is higher than between regions. On the regional scale, gene flow between subregions is higher than between populations within subregions. Generally, the genetic differentiation between populations within regions is higher for the mitochondrial RFLP data than for the allozyme data. These results suggest that most of the dispersal is female dominated and mostly takes place between populations within regions. Due to this extensive regional gene flow, local adaptation may be influenced by regional processes. This might have interesting implications for the coevolution of the predator C. crystallinus and its plankton prey.