['Blood eosinophils have mRNA for FcgammaRIIIB (CD16) but no or minimal spontaneous CD16 expression. Because IFN-gamma and chemotactic factors induce eosinophil CD16 expression in vitro, we postulated that blood eosinophils could express CD16.', 'Blood of nonallergic controls and subjects with allergic rhinitis, allergic and nonallergic asthma, or hypereosinophilia of various etiologies were analyzed for leukocyte CD16 surface expression.', 'CD16(+) eosinophils were identified on the basis of physico-optic characteristics, major basic protein, CD49b expression, and sorting by flow cytometry and microscope examination.', 'Subjects with allergic rhinitis and subjects with asthma had higher median percentages of CD16(+) eosinophils (8.1% [1% to 48.6%] and 7.3% [1.4% to 31.1%], respectively) than nonallergic controls and nonallergic asthmatics (3% [0% to 11%] and 4.6% [2.9% to 5.1%], respectively). In subjects with hypereosinophilia, CD16(+) eosinophils were increased only in a case of drug allergy. When subjects with mild allergic asthma were challenged with a relevant aeroallergen, blood CD16(+) eosinophils further increased during or after the late-phase response (6 to 48 hours after challenge; mean +/- SEM, 9.4% +/- 2.5% to 20.0% +/- 3.0%). CD16(+) eosinophils expressed more IL-5 receptor but less CD11b and IL-12p35 than did CD16(-) eosinophils.'] Does expression of FcgammaRIII ( CD16 ) on human peripheral blood eosinophils increase in allergic conditions?