In order to compare the diagnostic efficacy of the, basophil degranulation, RAST, indirect haemagglutination and latex tests, we carried out these four tests on 50 patients with confirmed hydatid disease due to Echinococcus granulosus. As a control group we employed 50 subjects who showed no evidence of hydatid disease or any other parasitic disease. The test which displayed the highest degree of diagnostic efficacy was the basophil degranulation test with a sensitivity of 93% and an accuracy of 97%. Next in diagnostic efficacy were the haemagglutination and RAST tests with very similar results-a sensitivity of 82% and an accuracy of 91% for the former, and for the latter a sensitivity of 80% and an accuracy of 90%. The latex test, with a sensitivity of 67% and an accuracy of 83%, possessed the lowest degree of diagnostic efficacy. There is an obvious decrease in the sensitivity of the tests when the localization of the cyst exclusively pulmonary; in these cases the RAST test was positive in only 50%, and the degranulation test in 77.7%.