An antigenic extract prepared from four different Mexican isolates of Trypanosoma cruzi cultured on BHI (three came from human cases-Agripina, Fidelfa and Ninoa, and other from triatoma-Cocula) were assayed with human sera. ELISA results always were consistent with clinical diagnosis. Sera from patients with a diagnosis of Chagas disease were reactive and non-chagasic sera were negative. Western blot of chagasic sera recognized antigens of molecular weight > 81 kd, 81 kd, 54 kd, 42 kd, and 26 kd. Sera with high OD in ELISA reacted with more peptide bands. The soluble extract antigens prepared from Mexican isolates of T. cruzi and from the Brazilian Y strain have an homogenous and similar reactivity.