CD23, the low affinity receptor for IgE, is a 45 kilodalton molecule belonging to the C-type lectin family, some members of which have been identified as adhesion molecules. Since it has been described upregulated in different cells in chronic inflammatory diseases and in rheumatoid arthritis in particular, where neutrophils are directly involved in tissue damage, our interest, in this work, has been focused on the expression and regulation of this antigen on neutrophil membrane. We studied 22 patients suffering from rheumatoid arthritis and 22 healthy control subjects. CD23 expression on neutrophil membrane was analyzed by immunofluorescence. Neutrophils of 9 out of 22 patients expressed CD23 molecules, neutrophils of 11 out of 22 patients expressed CD23 only after 24 h of incubation in RPMI; only 2 out of 22 patients did not express the CD23 antigen on neutrophil membrane either after isolation or after a 24 h incubation. On the contrary neutrophils isolated from healthy subjects did not express CD23 molecules upon isolation. Only in 7/22 control subjects neutrophils resulted positive after 24 h of incubation in RPMI. Moreover, we found that in our experimental conditions the presence of IFN-g or GM-CSF alone or in combination with IL-4 inhibited CD23 expression during the 24 h incubation. Our results show that there is a strong association between neutrophil ability to express CD23 and rheumatoid arthritis, and that such expression may be regulated by GM-CSF, IFN-gamma and IL-4.