In psittacine birds, the diagnosis of sarcocystosis is usually made on postmortem examination, and antemortem testing has been limited to muscle biopsy. We studied the applications of a serologic assay for antibody and plasma protein electrophoresis for changes in protein fractions in the antemortem diagnosis of sarcocystosis in psittacine birds. Several confirmed cases of sarcocystosis in psittacine birds were examined. To detect antibody, an indirect immunofluorescent assay was employed using Sarcocystis falcatula merozoites. Plasma samples from birds that demonstrated chronic neurologic signs had reactivity to the S falcatula antigen, and increases were found in the beta and gamma fractions by plasma protein electrophoresis. Conversely, in birds with the classic peracute onset of dyspnea and subsequent death, test results by either methodology were negative. These findings support the use of these 2 diagnostic tools as aids in the antemortem diagnosis of the nonperacute form of sarcocystosis in psittacine birds.