Early clinical diagnosis of invasive candidiasis is difficult. To facilitate rapid diagnosis of Candida infections, we developed an ELISA to quantitate levels of antibody to Candida mannan. The test was standardized by analysis of a nonselected inpatient population to determine a cutoff point defining the upper 5% of such a population as test-positive. Passively acquired sera from patients in intensive care units, patients with neoplastic disease or recent renal allografts, and other patients were analyzed. There was no significant difference between the number of positive tests obtained from patients in whom candidiasis was considered but cultures were negative and from the nonselected inpatient population. Positive tests were obtained from 18.5% of patients with Candida mucocutaneous colonization or infection and 40% and 63.6% of patients with probable and proven invasive candidiasis, respectively. Patients with neoplastic disease had lower test sensitivity than patients in other test categories. These results demonstrate the usefulness of a simple, rapid, standardized test for quantitation of levels of antibody activity to Candida mannan in the serodiagnosis of candidiasis.