We examined the biological characteristics of normodense and hypodense eosinophils prepared from the peripheral blood of the patients with allergic rhinitis caused by house dust mites by measuring leukotriene C4 (LTC4), platelet-activating factor (PAF), and superoxide anions. The normodense (density: 1.100-1.095) and the hypodense (density: 1.080-1.070) eosinophils were prepared by a Percoll density gradient. The normodense eosinophils produced a greater amount of LTC4 (15 ng/10(6) cells) after stimulation by calcium ionophore A23187 than the hypodense eosinophils (1.8 ng/10(6) cells). On the other hand, in the hypodense eosinophils higher amounts of both PAF (5210 pg/10(7) cells/15 min) and superoxide anions (0.33 nmoles/10(7) cells/min) were produced by calcium ionophore A23187 than in the normodense eosinophils, 501 pg/10(7) cells/15 min and 0.18 nmoles/10(7) cells/min, respectively. Considering these results, it is suggested that the two eosinophil subpopulations have distinct biological roles in generating these inflammatory mediators which appear as typical pathological features of allergic rhinitis.