Six dogs reared helminth-free were divided into 2 groups. Four dogs were infected per os with 200,000 protoscoleces each of Echinococcus granulosus and 2 were kept as uninfected controls. All the dogs were kept together until 32 days after infection, when 1 infected dog was killed, its intestine removed and the contents examined to confirm that the infection with E. granulosus had been successful. The remaining 3 infected dogs were transferred to high security housing and their feces inspected daily to establish the time infections became patent. The infected and control dogs were bled every 5 days for 75 days from the time of infection and the sera were stored at -70°C. Sera were tested by the enzyme-linked immunosorbent assay (ELISA) for antibodies to E. granulosus scolex excretory/secretory (ES) antigen, protoscolex antigen and oncosphere antigen. Antibodies to scolex ES antigen and protoscolex antigen were detected in the sera of infected dogs within 2 weeks of infection. Antibody titers rose rapidly and remained at a high level until the dogs were killed 75 days after infection. Antibodies in these sera did not cross react with antigens prepared from Taenia ovis, T. hydatigena, T. pisiformis, Ancylostoma caninum, Trichuris vulpis and Toxocara canis.