We evaluated basophil releasability in two groups of allergic patients with positive skin tests to Dermatophagoides pteronyssinus major allergen (Der p l) (29 adults with bronchial asthma and 17 with allergic rhinitis) and in 31 age-matched normal donors. Both basophil reactivity (maximal percent histamine release) and basophil sensitivity (the concentration that causes 50% of maximal percent histamine release: HC50) to Der p l in patients with asthma were similar to those in patients with allergic rhinitis. On the contrary, basophil reactivity to anti-IgE was significantly higher in patients with asthma (58.0 +/- 3.6%) than in patients with allergic rhinitis (46.3 +/- 5.2%; p less than 0.05). Both groups of patients showed an increased releasability compared to control subjects (27.3 +/- 4.6%; p less than 0.001), whereas there were no significant differences in basophil sensitivity to anti-IgE among the three groups of donors. Differences were also found with respect to basophil reactivity and sensitivity to f-met peptide, whereas no differences appeared when basophils from the three groups of donors were challenged with the Ca2+ ionophore A23187. There was a significant correlation between basophil reactivity and sensitivity to Der p l and to anti-IgE in both asthmatic and allergic rhinitis patients. A significant correlation was found between basophil reactivity and sensitivity to anti-IgE and serum IgE level only in patients with bronchial asthma, whereas no correlations were found in patients with allergic rhinitis. There was no correlation between in vivo mast cell releasability and in vitro basophil releasability in response to Der p l in either group of allergic patients.(ABSTRACT TRUNCATED AT 250 WORDS)