The importance of immunological arguments in the discussion of hydatidosis, the permanent increase of requirements, the risk of cross reactions, the frequency of sero-epidemiological surveys imply the utilisation of specific and rapid micro-methods. The technique of immunoelectrodiffusion on a cellulose acetate membrane answers partly to those criteria; we have used it since 1971 in the diagnosis of parasitic infections and mainly to that of hydatidosis. Two hundred cases (400 samples) of the latter were studied longitudinally and reported. This micro-method is very specific (co-immunoelectrodiffusion), equal to that of immunoelectrophoresis. Its rapidity (3 to 4 hours) is close to that of indirect immunofluorescence. The revelation of suggestive diagrams of fissuration underlines the relative emergency of the definitive interpretation of an immunological examination in the diagnosis of hydatidosis.