Upon exposure to a specific antigen, granulation of basophils bearing IgE disappears. The aim of this study was to assess the human basophil degranulation (HBD) test with hydatic antigen in 100 patients. Seventy patients were clinically suspected of having liver hydatidosis (LH) (group I). Eight patients had asymptomatic hepatic calcifications. Twenty-two patients had previous surgery for LH (group III). In group I the percentage of HBD was significantly higher in patients with LH (23 of 70) than in patients with other hepatobiliary diseases (P less than 0.001). In group II all patients had negative HBD tests. In group III the test became negative within 8-12 months after radical surgery in four patients, and remained positive in the other 18. These results suggest that the HBD test is useful for the diagnosis of LH. In asymptomatic patients with hepatic calcified cyst, a negative HBD test suggests a dead parasite. In previously operated patients, a positive test suggests persistence of antigen.