In children with perennial asthma, dual (immediate and late) reactions in the skin to D. pteronyssinus and Timothy grass pollen were more frequent with high doses of antigen and were associated with large immediate reactions. The frequency of dual bronchial or nasal reactions was not related to the size of the immediate reaction and dual reactions were commonly elicited to the lowest antigen dose which would elicit an immediate reaction. Serum IgG, IgA, IgM or IgE concentrations, IgE or IgG antibodies to the antigens and defective yeast opsonization did not differ in children with dual or immediate only reactions in skin, nose or lung. In five patients undergoing bronchial provocation tests with D. pteronyssinus there was no fever, no fine crepitations in the lungs and no significant change in the levels of C3.