We evaluated the formation of leukotriene C4 (LTC4) by peripheral blood eosinophils of different densities obtained from asthmatic and normal subjects. When stimulated with 1 microgram/ml of the calcium ionophore A23187 for 15 min at 37 degrees C, eosinophils with densities greater than 1.093 g/ml from asthmatic and normal subjects released 19.1 +/- 4.2 ng LTC4/10(6) eosinophils and 23.9 +/- 5.0 ng LTC4/10(6) eosinophils, respectively. In contrast, lower density eosinophils (densities 1.093 g/ml or less) isolated from the asthmatic subjects released significantly less LTC4 than did eosinophils of similar densities from normal subjects (41.6 +/- 3.0 versus 79.0 +/- 6.7 ng LTC4/10(6) eosinophils, p less than 0.05). Differences could not be demonstrated between the two subject groups in LTC4 metabolism, time course of extracellular release of LTC4, or dose response to A23187, nor were interactions between eosinophils and neutrophils with regard to LTC4 release evident. Thus, hypodense eosinophils elaborate greater quantities of LTC4 than do eosinophils of normal density whether obtained from normal or asthmatic subjects. However, the finding that peripheral blood eosinophils from asthmatic subjects have decreased capacity for the synthesis of LTC4 compared with cells of similar densities isolated from normal subjects demonstrates that the capacity of eosinophils to produce LTC4 is regulated by factors that are not necessarily reflected in the cell density.