Autoimmune polyglandular syndrome type I (APS I) is associated with chronic mucocutaneous candidiasis. To characterize the antibody responses in this subgroup of Candida albicans infections, we screened a candidal cDNA expression library with patient sera and found four cDNA clones encoding the immunopositive proteins enolase, heat shock protein 90, pyruvate kinase, and alcohol dehydrogenase. The reactivity to these antigens was studied further by immunoprecipitation assays with in vitro-transcribed and -translated proteins. Analysis of sera from 44 APS I patients showed that the highest antibody reactivity was found with enolase (80% of patients reactive), but significant serological responses were also found with heat shock protein 90 (67%), pyruvate kinase (62.5%), and alcohol dehydrogenase (64%). Overall, 95.5% of patients had detectable antibodies to at least one of these proteins. The cDNAs of enolase and heat shock protein 90 were also expressed in Escherichia coli and studied by immunoblotting. Again, 84% of sera reacted with enolase, whereas 44% of sera reacted with heat shock protein 90. A good correlation between the two methods was found for both enolase (r = 0.86; n = 58; P < 0.001) and heat shock protein 90 (r = 0.71; n = 56; P < 0.001). Our results indicate that the four abundant candidal proteins are the major antigens and can be used as accurate markers of candidiasis in APS I patients. The immunoprecipitation assay described here is particularly useful for the rapid analysis of a large number of samples.