Indirect fluorescent antibody tests were performed with sera of paragonimiasis patients and skin test positive sera against Paragonimus antigen. Paragonimus antigen was prepared from lyophilized adult worms of P. westermani by defatting with ethyl-ether before extracting with barbital buffered saline. Preparation of Paragonimus antigen for the indirect fluorescent antibody test was based upon Sato's method used for sero-diagnosis of anisakiasis, with Sephadex G-25 instead of Sepharose 4B. The results were as follows: The indirect fluorescent antibody titers of paragonimiasis patient's sera ranged from 1:64 to 1:512, whereas the control sera showed titers of less than 1:16. As controls, Clonorchis patient's sera and parasite-free healthy human sera were used. In indirect fluorescent antibody tests, the skin test positive human sera against Paragonimus antigen showed a positive rate of 41.5 per cent in the case of titers more than 1:40. On the other hand, complement fixation tests on the same sera showed a positive rate of 32.5 per cent in the case of titers more than 1:20.
