The antibody activities against Aspergillus fumigatus and Candida albicans by indirect hemagglutination (IHA) and counterimmunoelectrophoresis (CIE) were examined twice at a month's interval in 251 sera from 169 male and 82 female patients admitted to the Higashi Nagoya National Hospital for pulmonary diseases. The patient population was composed of 226 patients with active or cured pulmonary tuberculosis including 25 patients complicated with pulmonary aspergillosis and 25 other lung diseases. In our tests, antigens used were crude supernatants of culture-broth which are the generous gifts of Torii Pharmaceutical Company. The antibody activity against Aspergillus by IHA was positive in 2.9% of the sera in the first and in 0.9% in the second test and was positive against Candida by IHA in 44.9% in the first and in 44.0% in the second test (Table 1). As regards patients with pulmonary tuberculosis, the population whose serological reaction was positive against Candida did not increase with age (Table 2). Two results of the antibody activities against Aspergillus and Candida by CIE were the same. The CIE results were positive in 19.5% against Aspergillus and in 16.3% against Candida (Table 3). In CIE test, 4.3% were positive against both Aspergillus and Candida. The causes of high positive rate in IHA against Candida may be due to (1) difference in the antibody, namely, antibody measured by IHA mainly composed of IgM and that by CIE composed of IgG and (2) difference in the virulence between Candida and Aspergillus.(ABSTRACT TRUNCATED AT 250 WORDS)