We studied the serodiagnosis of human hydatid disease using the dot-enzyme-linked immunosorbent assay (dot-ELISA) and the indirect hemagglutination assay (IHA). Hydatid cyst fluid antigens from sheep were highly reactive against a battery of positive human sera. Moose-derived antigen was less reactive, whereas human- and camel-derived antigens showed nonspecific false-positive reactions. Sensitivity of the Dot-ELISA was 96% using sheep-derived antigen and 45 human sera from 43 surgically proven cases of hydatidosis disease caused by Echinococcus granulosus, E. multilocularis and E. vogeli. The IHA test reacted with 100% of patient sera (P = N.S.). Specificity of the dot-ELISA was 98%; one false-positive reaction was observed in the dot-ELISA when 52 sera from healthy subjects were assayed. Cross-reactions were observed with sera from patients with cysticercosis, filariasis, toxocariasis, trichinosis, visceral larval migrans, and liver cirrhosis. Of 204 sera tested in duplicate, 191 (94%) did not vary more than one twofold titer dilution. The dot-ELISA is rapid and as sensitive as the IHA test in the diagnosis of hydatidosis. In addition, unlike other currently performed tests for hydatid disease, this rapid and economical enzyme immunoassay is very antigen-conservative, requiring only nanogram quantities of parasite antigen, and very serum conservative, needing only 50 microliter of diluted patient serum.