Summary The complement-fixation (CF) test, the indirect hemagglutination (IHA) test, and the latexflocculation (LF) test were evaluated for the detection of Echinococcus antibody in serum from 27 proved cases of Echinococcus infection in man. In addition, the specificities of the three tests were evaluated against serum from 45 persons with non-Echinococcus diseases and with serum from 40 apparently healthy blood donors. The IHA test was more sensitive (92.5% of the serum from 27 cases of Echinococcus infection) than the LF test (80% of 20), or the CF test (77.7% of 27). The IHA and the LF tests were more specific in that no false positive reactions occurred. Two false positive reactions did occur in the CF test. The results of this study indicate that the IHA test is the most sensitive and reliable test for the detection of Echinococcus antibody in infected human beings. The LF test proved almost as good. The ease of performance plus the sensitivity of these two tests make them preferable to the CF test for the serologic testing of serum for Echinococcus antibody.