Echography and/or chest radiograph in association with six serologic (immunologic) methods were tested for their ability to diagnose human hydatidosis. The immunologic techniques used were latex agglutination, counter immunoelectrophoresis, enzyme-linked immunosorbent assay (ELISA) with whole hydatid fluid and with antigen 5, a thermobabile lipoprotein that elicits the arc 5 precipitin line in immunoelectrophoresis. In this report, the results of examinations of 273 patients are presented. Of these, 243 cases were surgically proven to have hydatidosis, whereas 30 of the 273 that were strongly suspected of having hydatid cysts by radiology were shown to have other pathologies. The ELISA was more sensitive than the other methods, with 204 of 243 sera shown to be positive. The remaining 39 sera that gave false-negative results were tested using two recently developed methods, enzyme-linked immunoelectrodiffusion assay (ELIEDA) and immunoblotting (electrophoretic migration of hydatid fluid antigens under denaturing but nonreducing conditions, blotting, and immunoenzymatic assay). Immunoblotting, using our experimental conditions, had a greater sensitivity than the ELIEDA with this technique. Four of 37 sera showed one to three bands of 65, 12, and 8 kD. The sensitivity of the ELISA did not increase with either the size or type of cyst. Comparison of radiology with serology confirmed a good correlation between the two methods. Nevertheless, serology is more specific but less sensitive than imagery.