To evaluate the immature eggs of Paragonimus westermani as a source of diagnostic antigen, about a million eggs which were excreted by 104 adult worms were collected; their saline extract(soluble egg antigen; PwSEA) was prepared. The specific IgG and IgM antibody levels were observed in experimental dog paragonimiasis by micro ESISA, using PwSEA as well as whole worm extract of 12 week-old P. westermani(PwWWE). The protein composition of the PwSEA was observed by disc-PAGE. The results could be summarized as follows: 1. Specific IgG antibody to PwSEA begant to increase on 8 weeks after the experimental infection; it maintained its high level until the observation period of 13 weeks. The levels of IgM antibody to PwSEA however, did not show any significant change. 2. Specific IgG antibody to PwWWE began to increase earlier from 2 weeks after the infection and continued to increase until the observation period of 13 weeks. Its level was much higher than that to PwSEA. Specific IgM antibody to PwWWE increased temporarily during 2-8 weeks after the infection. 3. By disc-PAGE, PwSEA showed 2 protein bands of very low motility. The bands of PwSEA corresponded to the frist and second bands in the electrophoretic pattern of PwWWE of the 12 week-old worms. The above results indicated that the PwSEA induced antibody production in dog paragonimiasis, but its antigenicity was weaker than PwWWE to be used as a diagnostic antigen.