Biomphalaria tenagophila and B. straminea snails bred from snails collected at 8 counties of Minas Gérais, Brazil, were infected with Schistosoma mansoni miracidia of the strains LE and SJ. The percent experimental infection range was 0-28% for B. tenagophila and 0-21% for B. straminea. These results were compared with the ones by other authors showing that more than 70% of 32 populations from Minas Gerais (12 populations of B. tena- gophila and 20 of B. straminea) were suscep- tible to experimental infection with S. mansoni. These experimental data together with reports claiming the finding of naturally S. mansoni infected B. tenogophila and B. straminea at four localities since 1982 seem to indicate the existance of favourable conditions to the pre-adaptation to parasitism, as no infected snails had been found in these regions before. This adaptation has been described to occur in São Paulo and in brazilian northeastern region. These data are important to the control of the dissemination of schistosomiass to undamaged areas, as these two species of Biomphalaria are widely distributed in Brazil.