OBJECTIVE: Elevated serum lgE and pheripheral blood eosinophilia are immunologic hallmark in helminthic infections. Recently, these responses are known to be regulated by Th2-specific cytokine IL-4 and IL-5, respectively. And also, the antagonistic effects of IFN-gamma on Th2 cell proliferation were shown in vitro. However, few studies on the effect of IFN-gamma on Th2 cytokine responses in Paragonimus westermani infection are reported, In this study, effects of rIFN-gamma on serum lgE production and the number of pheripheral blood eosinophils in mice infected with P.westermani were examined. METHODS: 5-6week old male BALB/c mice treated with IFN-gamma were divided into 3 groups. All the mice were inoculated orally with 20 metacercariae of P.westermani. GroupImice(0-14days) were treated intraperitoneally with 2x10(3) unit of rIFN-gamma at daily intervals from the time of the infection to 4th day infection, group II mice(5-14 days) were treated with rIFN-gamma from the 5th to the 14th day of infection and group III mice(8-14 days) were treated from the 8th to the 14th of infection. Total serum lgE and the number of pheripheral blood eosinophils were examined in infected mice treated with rIFN-gamma. RESULTS: The serum lgE levels in groupIand II were decreased compared with those of infected mice with no treatment with rIFN-gamma, but not significantly. The number of pheripheral blood eosinophils in group I and II were decreased compared with those of infected mice with no treatment with rIFN-gamma, especially significant(p<0.05) reduction was shown in group I. However, the serum lgE levels and number of pheripheral blood eosinophils in group III were similar to those of infected mice with no treatment with rIFN-gamma. CONCLUSION: These results suggest that IFN-gamma decreases Th2 cytokine response in P.westermani-infected mice. However, IFN-gamma treatment has less of an effect once the production of Th2-associated cytokines has become established.