Fil: Kamenetzky, Laura. ANLIS Dr.C.G.Malbrán. Instituto Nacional de Enfermedades Infecciosas. Departamento de Parasitología; Argentina.Fil: Muzulin, Patricia Marcela. ANLIS Dr.C.G.Malbrán. Instituto Nacional de Enfermedades Infecciosas. Departamento de Parasitología; Argentina.Fil: Gutiérrez, Ariana M. ANLIS Dr.C.G.Malbrán. Instituto Nacional de Enfermedades Infecciosas. Departamento de Parasitología; Argentina.Fil: Angel, Sergio O. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto Tecnológico de Chascomús; Argentina.Fil: Zaha, A. Universidade Federal do Rio Grande do Sul. Instituto de Biociências. Centro de Biotecnologia e Departamento de Biologia Molecular e Biotecnologia; Brasil.Fil: Guarnera, Eduardo A. ANLIS Dr.C.G.Malbrán. Instituto Nacional de Enfermedades Infecciosas. Departamento de Parasitología; Argentina.Fil: Rosenzvit, Mara C. ANLIS Dr.C.G.Malbrán. Instituto Nacional de Enfermedades Infecciosas. Departamento de Parasitología; Argentina.Echinococcus granulosus antigen B (AgB) is encoded by a gene family and is involved in the evasion of the host immune response. E. granulosus exists as a number of strains (G1-G10) that differ in biological characteristics. We used PCR-SSCP followed by DNA sequencing to evaluate sequence variation and transcription profile of AgB in 5 E. granulosus strains. Twenty-four genomic sequences were isolated and clustered in 3 groups related to 2 of the 5 reported AgB genes. AgB4 genes were present in almost all strains, whereas AgB2 were present as functional genes exclusively in G1/G2 cluster, and as non-functional genes in G5 and the G6/G7 cluster, suggesting inter-strain variation. The AgB transcription patterns, analysed by RT-PCR, showed that AgB2 and AgB4 genes were transcribed in G1, while only the AgB4 gene was transcribed in G7 strain. Cysts from the same strain or cluster shared more genomic and cDNA variants than cysts from different strain or cluster. The level of nucleotide and deduced amino acid sequence variation observed is higher than that reported so far for coding genes of other helminths. Neutrality was rejected for AgB2 genes. These data show the genetic polymorphism of antigen-coding genes among genetically characterized strains of E. granulosus.