Chagas' disease or American trypanosomiasis is a parasitic zoonosis which constitutes and important public health problem in most of the Latin American countries. According to the development of socio-political events in the world, it is possible at present to speak of rural-periurban Chagas' disease and urban Chagas' disease. Rural-periurban Chagas' disease. In its endemo-enzootic condition it is distributed in vast areas from Mexico in the north and Argentina and Chile in the south. It is calculated that the population at risk is about 90 million persons, not less than 16-18 million are Trypanosoma cruzi infected and approximately 38% of these present or have presented pathology caused by the parasite. Organs most frequently affected: heart, esophagus and colon. The corresponding biological vectors are hematophagus triatomid bugs, with greater than 100 species synantropic (st) or sylvatic (sv), existing between parallels 41 N. and 46 S., but only about 36, which have been found infected, have some relationship with man because their adaptation to human dwelling. The human parasitose is less extended due to the fact that the vectors of the region are predominantly sv. The known reservoirs are more than 180 species of terrestrial mammals: domestic, st and sv. Man is possibly the most important. Some available relevant epidemiological information is summarized as follows: Additionally, some autochthonous cases of T. cruzi human infection have been registered in the United States, Trinidad-Tobago, Guyana and Belize. Moreover, infected vectors and/or sv reservoirs have been observed in almost a dozen of Caribbean countries. Urban Chagas' disease. As a consequence of possible better salaries and many other motivations, in the last decades there have been significant and constant migrations from rural to urban areas in many Latin American countries. This situation has facilitated the dissemination of T. cruzi infection through infected reservoirs--mostly humans--and/or passively transported infected vectors. In most of the cases these rural-urban migrations occur in chagasic endemic areas within a same country or in neighbouring ones; in others, the migration can involve countries where Chagas' disease does not exist, transmission being via blood transfusion or placental. According to some estimates, with a mean rate of 1.5% chagasic infected blood donors the minimum risk of T. cruzi transmission is nearly 12.5-25.0% when the volumen of transfused blood is 500 ml.(ABSTRACT TRUNCATED AT 400 WORDS)