We performed an epidemiological survey of 17 thermal baths and the same number of mud-basins. This study aimed to ascertain the presence and incidence of small free-living amoebae, particularly species and/or strains of Naegleria and Acanthamoeba spp., occasional etiological agents of fatal meningoencephalitis and/or ocular infections in man. Over 51 samples of water and mud incubated at 37 degrees C and at 45 degrees C, 34 (66.7%) became positive at 37 degrees C and 33 (64.7%) at 45 degrees C. We isolated 7 (6%) strains of Naegleria spp., 6 (5.2%) of Acanthamoeba spp., 39 (33.6%) of Vahlkampfia spp., 28 (24.1%) of Hartmannella spp. and 36 (31.1%) strains of other species of free-living amoebae. 4 strains of Naegleria spp. and 6 of Acanthamoeba spp. proved pathogenic both in vivo, after experimental infection (meningoencephalitis) in the albino mouse, and in vitro, having previously contaminated monolayers of Vero cell line (cytopathic effect). Within the isolated pathogenic strains of Naegleria spp., a new strain of N. australiensis s.sp. italica was typified from an immunochemical point of view. This should be added to previous isolations reported by us.