The prevalence of fungal complement-fixing antibodies in sera from 58 patients with sarcoidosis was determined and compared to complement-fixing antibody titers in 50 sera from a normal control group and 50 antinuclear antibody-positive sera. Sera from 9 patients with sarcoidosis had complement-fixing antibody titers greater than 1:8 to Histoplasma yeast antigen; serum from one normal control subject had a titer greater than 1:8; and none of the antinuclear antibody-positive sera demonstrated titers greater than 1:8. There were no significant complement-fixing antibody concentrations observed against histoplasmin, blastomycin, and coccidioidin antigens in any serum from the 3 groups studied. The increase in antibody titers to the Histoplasma yeast antigen might have been related to the generalized increase in immunoglobulin concentrations noted in patients with sarcoidosis.