Specific serum IgE levels of Clonorchis sinensis in infected humans were measured by avidin-biotin ELISA, and allergens from C. sinensis were identified by immunoblot and autoradiography. Then, allergens fractionated by Sephadex G-200 gel filtration were analyzed, and cross-reactive allergenic components of C. sinensis reacted with paragonimiasis sera were revealed. Fourteen out of 15 C. sinensis egg-positives were found to be serum IgE positive (absorbance > 0.27). Of 14 IgE-reacting allergen bands visualized, major allergens of 66, 61.5, 45, 37, 28.5, 23.5 and 15.5 KD were recognized by more than 50% of the sera of infected humans. The considerable individual variations of IgE immune responses to C. sinensis allergenic components were also noticed. C. sinensis extract was separated into 5 fractions by Sephadex G-200 gel filtration. Seventy-four KD allergen was recognized in the first fraction, 50, 45, 37, 29.5 and 28.5 KD in the third, and 15.5 KD in the fourth. Cross-reactive allergens with sera of paragonimiasis cases were identified as 66, 45, 28.5, 13 and 7.5 KD.