To study the changes of IL-2 and TNF-α in serum and the IL-2 secreted by peripheral blood lymphocytes of goats infected with Fasciola hepatica,thirty six clinically healthy white goats were randomly divided into groups coded as Ⅰ,Ⅱ,Ⅲ,every 12 goats.Goats in group Ⅰ and Ⅱ were inoculated with a single oral dose of 200 and 500 encysted Fasciola hepatica metacercaria,respectively,while those in group Ⅲ were untreated controls.Blood samples were collected from the jugular vein once a week for 11 weeks.Changes in the serum levels of IL-2 and TNF-α and the ability of peripheral blood lymphocytes to secrete IL-2 were detected.Serum IL-2 levels decreased in group I,but increased in group Ⅱ.The levels of TNF-α and secreted IL-2 were elevated by varying degrees in both groups Ⅰ and Ⅱ.Lymphocytes displayed reactivity during the first week after infection with a significantly increased response to both specific and non-specific challenges.TNF-α may be involved in the hepatic injury process caused by Fasciola hepatica.The infective dose of Fasciola hepatica greatly influenced IL-2 levels in the host playing a vital role in the initiation of host defense.