It has been reported that blood basophils comprise two populations of different densities. In this study, we compared the responses of two populations of basophils (band-1 and 2 basophils) to several secretagogues and anti-allergic agents. Twelve patients with bronchial asthma, 3 patients with Japanese cedar pollinosis and 6 healthy subjects were included in this study. Band-2 basophils collected from the interface between Percoll of density 1.078 and 1.068 g/ml released histamine better in response to anti-IgE than band-1 basophils taken from the interface between plasma and Percoll 1.068 (band 1 vs. band 2, 13.2 +/- 2.7 vs. 21.4 +/- 3.6% at 1:10(5), p less than 0.01; 47.1 +/- 5.0 vs. 57.7 +/- 6.1% at 1:10(4), p less than 0.01). Band-2 basophils also responded better to formyl-methionyl-leucyl-phenylalanine than band-1 basophils (34.4 +/- 4.9 vs. 43.2 +/- 5.6% at 10(-6) M, p less than 0.01; 35.6 +/- 5.0 vs. 45.2 +/- 5.7% at 10(-5) M, p less than 0.01). In contrast, band-1 basophils were much more sensitive to the calcium ionophore A23187 stimulation than band-2 basophils (13.0 +/- 3.7 vs. 6.3 +/- 1.8% at 0.05 microgram/ml, p less than 0.05; 52.5 +/- 4.3 vs. 33.8 +/- 3.9% at 0.1 microgram/ml, p less than 0.01; 71.3 +/- 3.3 vs. 51.5 +/- 4.2% at 0.2 microgram/ml, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)