New levels of reproducibility and sensitivity have been achieved in the detection of anticysticercus antibodies in human sera by using cysticercus vesicular fluid as the source of antigens for both ELISA and hemagglutination assays. Reproducibility both between tests on a serum and between similar sera was significantly improved over typical results using antigens from whole parasite extracts. Sera collected from uninfected individuals in endemic areas gave somewhat elevated values over those collected in nonendemic areas. This necessitated the use of a higher threshold in endemic areas to avoid false positives. With the threshold appropriate for a nonendemic area, both ELISA and hemagglutination were sensitive enough to detect infection in 95% of cases. With the threshold value for sera from an endemic area, these sensitivities were reduced to 80%-90%. A prominent 103-Kd protein of vesicular fluid, not related to antigen B, elicited the strongest antibody response in neurocystercotic patients.