Serological diagnosis of alveolar hydatid disease using crude parasite antigen is problematical with the result that several groups have addressed the question of specific serodiagnosis using defined native or recombinant antigens. Sequence data are available for two lambda gt 11 cDNA clones, designated EM4 and pEM10, which express E. multilocularis species-specific proteins in immunodiagnostic assays using human sera. Here, we have drawn attention to the extensive similarities between these antigens and have compared their characteristics since both may prove valuable in the future diagnosis of alveolar hydatidosis.