The behaviour of IgE antibodies was investigated by the micro-ELISA method (IgE-ELISA) in patients affected by hydatidosis or in patients who had already been operated on. The results were correlated with those obtained by IgG-ELISA, IgM-ELISA, IgA-ELISA and IHA tests. In the preoperative phase the IgG-ELISA method proved to be as sensitive (80%) as the IHA test (78.5%); the IgE-ELISA method showed a good sensitivity (72.8%) with a positive rate for the IgE-ELISA/IHA of 92.7%. The IgM- and IgA-ELISA methods were of moderate sensitivity. The IgE-ELISA proved to be much more suitable than the other methods for postoperative control, since the persistence of positivity 4 years after surgery suggests the involvement of a relapse.