Abstract: An indirect ELISA for the sero-diagnosis of hydatidosis was described. The antigen used was lung hydatid cyst fluid treated with activated charcoal.The optimal conditions for the test were: antigen 10 μg/ml and the suitable dilution of antibody 10-1 to 10-5. Positive results were obtained from all the 25 surgically confirmed hydatidosis cases (reading 0.930±0.450), while the sera of 30 healthy control were negative (reading 0.119±0.055).The specificity of this method was demonstrated by both the replacement test and the block test. In addition, ELISA was superior in sensitivity to counter electrophore-sis and complement fixation test. However, it showed 7.4% false positivity and cross-reactions with tuberculous or hepatitis sera.