Circulating immune complexes (CIC) were determined from dog-allergic asthmatic children (n = 35) receiving immunotherapy with dog dander and hair extract. The results from CIC are expressed in SDU (standard deviation units) and presented as follows: pretreatment results (n = 20), rush results (n = 11), mid-schedule results (n = 20), maintenance results (n = 15) and the results of the placebo-treated group (n = 12). The results of the placebo-treated group (n = 12) and those of the untreated atopic (n = 12) and non-atopic (n = 14) were controls. CIC levels were analysed by means of KgB-ELISA (conglutinin binding enzyme linked immunosorbent assay), C1qB-ELISA (C1q-binding enzyme linked immunososrbent assay), RFb-ELISA (rheumatoid factor binding enzyme linked immunosorbent assay) and by PIPA (platelet 125J-labelled staphylococcal protein-A test). The CIC level determined by KgB-ELISA in dog-allergic asthmatic children was higher than that of the atopic controls (P less than 0.05) already before the onset of the hyposensitization. During conventional hyposensitization with dog dander and hair the CIC level remained the same as before treatment. On day 5 of rush hyposensitization the mean level of CIC showed no increase when compared with the pretreatment values. A statistically significant correlation (P less than 0.01) was observed between the dog dander and hair-specific IgG antibodies and the CIC level measured by KgB-ELISA during the maintenance period of conventional immunotherapy. The samples of sera to measure this correlation were collected before the injection of allergen and after 2 weeks of injection during maintenance treatment.(ABSTRACT TRUNCATED AT 250 WORDS)