Six Trypanosoma Cruzi Paraguayan strains, isolated from accute chagasic patients, were studied by their behaviour in Bald/C mice, metacylogenesis, biometry of metaciclic froms and lectin agglutination. Early, intermediate and late parasitemic peaks were observed and the strains did not show high virulence. Metacyclogenesis capacity was not higher than 50 percent in all cases, and there were no big differences inthe biometry and lectin agglutination assays. Although previous schizodeme analysis of these strains showed rather homogeneous profiles, biological feautures were quite heterogeneous