SummaryMeasurements by radiometric assay of specific IgE, IgA, IgM, igD and IgG antibodies, in fifty‐six patients with asthma, fifty‐six with rhinitis and twenty with allergic bronchopulmonary aspergillosis (ABPA), showed differences in the patterns of antibody response between the three patient groups, both in terms of levels of class specific antibodies and the proportion of patients giving positive results.Specific IgE antibody values were similar in all three groups and positive results were found in three‐quarters of the patients in each group. No other class of antibody toCandida albicansgave values which were similar in all three patient groups.Specific IgG and IgA antibody values were highest in ABPA and lowest in rhinitis; specific IgM antibody values were highest in asthma and lowest in ABPA; specific IgD antibody values were higher in rhinitis than asthma and very low in ABPA.Specific IgG1 and lgG2 antibodies to C.albicanswere higher in rhinitis than in asthma, whereas specific IgG3 and lgG4 values were significantly higher in asthma than in rhinitis.There was a greater number of positive results for IgG1, IgG2 and IgG4 in patients with ABPA than in the other two patient groups where values for IgG1 and IgG2 antibody toC.albicanswere mainly negative. Positive IgG3 antibody results occurred with greatest frequency in patients with asthma, half of them giving values greater than the mean + 2 s.d. of the control value; positive specific IgG4 antibody values occurred more frequently in asthma than in rhi