Trypanosoma cruzi is classified into two major groups named T. cruzi I and T. cruzi II. In the present work we analyzed 16 stocks isolated from human cases and four isolated from triatomines from diverse geographical origins (Mexico and Guatemala). From human cases four were acute cases, six indeterminates, and six from chronic chagasic cardiophatic patients with diagnosis of dilated cardiomyopathy established based on the left-ventricular end systolic dimension and cardiothoracic ratio on chest X-radiography and impaired contracting ventricle and different degree conduction/rhythm aberrations. DNA samples were analyzed based on mini-exon (ME) polymorphism, using a pool of three oligonucleotide for the amplification of specific intergenic region of T. cruzi ME gene.All the Mexican and Guatemalan isolates regardless their host or vector origin generated a 350 bp amplification product. In conclusion T. cruzi I is dominant in Mexico and Guatemala even in acute and chronic chagasic cardiopathy patients. To our knowledge, this is the first study describing predominance of T. cruzi I in human infection for North and Central America. Key words Trypanosoma cruzi -mini-exon -Mexico -lineage I -GuatemalaTrypanosoma cruzi is classified into T. cruzi I and T. cruzi II, this denomination aroused from a consensus reached by specialists based on different markers (Satellite Meeting 1999). T. cruzi I is mainly observed in wild mammals and more adapted to marsupials and sylvan triatomines, it is only occasionally isolated from humans, whereas T. cruzi II is apparently more associated with primates and it is usually found in human infections. Until now all parasites that have been isolated from seropositive individuals in Brazil belong to T. cruzi II (Fernandes et al. 1998. Recently a published report paper show a predominance of lineage I in 56 Mexican T. cruzi stocks isolated from vectors, humans, and sylvatic mammals using RAPDs, but the clinical status of human cases was not identified (Bosseno et al. 2002). In South-America also was found in 23 isolates from acute chagasic patients using ribosomal and miniexon (ME) marker that 74% of them belonged to T. cruzi I (Anez et al 2004). It is known that the ME gene is presented in the nuclear genome of all Kinetoplastida in nearly 200 copies in tandemly-repeated sequences. This gene consist of three regions: exon, intron, and intergenic region. The exon is highly conserved, the intron is moder- ately conserved and the intergenic region or non-transcribed spacer is particular dissimilar. This feature has allowed the classification of T. cruzi in two main groups (Devera et al. 2003, Macedo et al 2004.In the present work we analyzed 16 stocks isolated from human cases and four isolated from triatomines all from with diverse geographic origins (Mexico and Guatemala). Seven came from Guatemala and 13 from Mexico.Six were isolated from chronic chagasic cardiopathyc (CCC) patients who were evaluated at Instituto Nacional Cardiología "I. Chávez" in Mexico. All of them have been diagnosed ...