Anti-Clonorchis IgG antibody levels in serum were observed by ELISA in 129 egg positive cases and in 25 controls. The antibody levels were 0.063 to 1.216 (0.325+/-0.202)in clonorchiasis cases and 0.078 to 0.670 (0.255+/-0.133) in controls. The difference was statistically significant. However, serological diagnosis of clonorchiasis was not satisfactory in lightly infected cases because of low levels of specific IgG antibody. The antibody levels were well correlated with EPG. Changes of the IgG antibody levels were not significant 12-14 days, 4 weeks and 8-9 weeks after praziquantel treatment. Seven and 13 months after treatment, the IgG antibody levels were lowered significantly. The period for serologically negative conversion after praziquantel treatment was between 9 weeks and 7 months in human clonorchiasis.
