The aim of this study was to investigate immune responses as a result of infection with the parasitic helminth, Fasciola hepatica. Analysis of IL-4 and Interferon-y cytokines described a predominant type 2 immune response in BALB/c mice infected with metacercana of F hepatica Levels of IL-4 mRNA assessed by reverse transcnption-polymerase chain reaction (RT-PCR) provide the first evidence that the immune response becomes polarised 1 day post infection. We also investigated immune responses to F hepatica derived antigens IL-4 and Interferon-y cytokine production revealed a polarised type 2 response m BALB/c mice immunised with F hepatica excretory/secretory (ES) products. As type 1 immune responses have been associated with protection against infection with F hepatica (Mulcahy et a l , 1998), we established a polarised type 1 immune response in BALB/c mice by immunising with cathepsm L in combination with various adjuvants.