Previous studies support the possible application of galactomannan, a major antigen of Aspergillus sp., to aspergillosis diagnosis in avian and other animal species. An assay is commercially available for use with human serum and bronchoalveolar lavage fluid samples. In the current study, galactomannan results from plasma samples were compared between birds with histologically confirmed aspergillosis and those that were clinically normal presumptively non-Aspergillus infected birds per submitting practitioners' responses to a questionnaire. It was observed that infected birds demonstrated a 2.6-fold increase in galactomannan over birds without evidence of aspergillosis. With the use of a galactomannan index of 0.5 as a cutoff, the sensitivity and specificity of the test were found to be 67% and 73%, respectively. In addition, plasma samples were analyzed for abnormalities in protein electrophoretic patterns. Infected birds had a higher incidence of increased beta and/or gamma globulin concentrations. Test sensitivity and specificity were 73% and 70%, respectively. If the 2 tests were used as a panel, then the sensitivity was 89% and specificity was 48%. These data indicate that both galactomannan and protein electrophoresis may be valuable tools in the diagnosis of avian aspergillosis.