Delayed cutaneous reactivity to Candida albicans (C. albicans) and PPD (purified protein derivative) was examined in 52 patients with bronchial asthma in relation to the production of specific IgG4 antibodies against the antigen. 1. The frequency of a positive, immediate skin reaction to C. albicans was similar among the five age groups, ranging from 60.0% to 66.7%. 2. The incidence of a positive delayed skin reaction to C. albicans was lower in patients between the ages of 10 and 30 and tended to decrease with aging in the patients over the age of 51. 3. A delayed skin reaction to PPD was positive in patients between 31 and 50 with a higher incidence; this incidence decreased in patients over age 51. 4. The level of C. albicans-specific IgG4 antibodies was significantly higher (26.7 u/ml) in patients with a negative delayed skin reaction to the antigen than in those with a positive reaction (5.9 u/ml) (p less than 0.001). There was no correlation between delayed skin reaction to PPD and production of specific IgG4 antibodies.