Polypeptide antigen as isolated from adult worms of Clonorchis sinensis by means of diluted HCl-extraction method. Preliminary intradermal examination with those polypeptide antigen(CPT) were performed on patients of clonorchiasis, paragonimiasis and metagonimiasis and the result of the intradermal test with CPT antigen were compared with those of Clonorchis protein fraction(CPF) and Veronal buffer saline extraction (VBS) antigen. The result of the examination were summerized as follows: 1. When 0.05 ml (1 microgram) of CPT was injected intradermally, the positive intradermal reaction appeared in 42.7 per cent (37 of 82) on the patients of clonorchiasis. 2. The sizes of the wheal and erythema with CPT antigen was smaller than that of CPF and VBS antigen. 3. Intradermal reaction with CPT antigen was carried out for other parasitic diseases, such as paragonimiasis and metagonimiasis. The result indicated that CPT antigen may be showed no cross reactions. 4. Clonorchiasis pateints who with negative reaction to CPT antigen, reacted negatively to CPF and VBS antigens.