Up the present, the works of collecting planorbids done in 226 municipalities for the elaboration of the geographical distribution chart in the State of São Paulo (Brazil), showed the presence of two intermediate host species of Schistosoma mansoni: Biomphalaria tenagophila and Biompralaria glabrata. Although the technicians from the Psiculture Stations, have not found snails in the water inside the containers used for the transportation of fishes, the ecological conditions of B. straminea in the latest researches are such as to indicate that they have been introduced, in our State through fish transportation imported from areas where it occurs, such as the State of Amazonas and Ceará (Brazil). The aim of the importation of these fishes is its adaptation to local waters. The occurrence was noticed in the Psiculture Stations of the towns of Barra Bonita and Americana, and in an aquarium of a private house in the city of São Paulo. This shows the danger that the distribution of fishes represents and the way it is being done. The seriousness of the problem originates not only from the importation of the said species but also from its dissemination in the State, through the redistribution to the private Psiculture Stations. It should be remembered that this dissemination can be also done through rivers in which banks are located tanks for the breeding of fishes as mentioned before. This facts was communicated to the National Department of Rural Endemies for the necessary measures. One of the steps to be taken should be the quarentine for fishes from zones infested with species of planorbids hosts of S. mansoni. The passive scattering of B. straminea by the transportation of fishes, will enlarge the geographical distribution of these planorbids,which have already been found in Venezuela, Guianas and Brazil. In this last country it is found in all its States with the exception of Rio Grande do Sul, Santa Catarina, Rio de Janeiro and Federal Territories. Two hundred and seventeen specimens of B. straminea were examined and all of them were negative to cercaries of Shistosoma mansoni.