A simple method for isolating highly purified eosinophils from human blood is described. Buffy coats from normal individuals (eosinophil counts less than 0.4 x 10(9)/litre) were centrifuged through a two layer Percoll density gradient, to produce a granulocyte fraction containing neutrophils and eosinophils. Neutrophils were extracted from this fraction using a monoclonal antibody (CLB FcR gran 1) against CD 16 (Fc gamma R III) in a direct or indirect selection procedure using immunomagnetic beads (Dynabeads). This negative immunoselection produced eosinophils of greater purity and with a superior capacity to mount a respiratory burst than eosinophils isolated by a method employing metrizamide.