The distribution in the environment of Naegleria fowleri, the causal agent of primary amoebic meningoencephalitis has been investigated in this study. N. fowleri was isolated only from a thermally polluted canal. These amoeboflagellates were not isolated from another thermally polluted canal in the neighbourhood indicating that, apart from high temperature, other factors are involved in the selective proliferation of N. fowleri. This species was absent in all other samples originating from two canals, a stream, two lakes, several reservoirs and slow sandfilters of a water supply service and also a water distribution network. Many other amoebae able to grow at 42° C. were found in different places. Most of the N. fowleri strains isolated were not virulent for mice, although they showed all the characteristics of the pathogenic strains.