The carcinoembryonic Ag (CEA)-like glycoproteins present on human granulocytes have been designated non-specific cross-reacting Ag (NCA). We have recently demonstrated that granulocyte-specific CD66 and CD67 mAb recognize the three originally described NCA. CD66 binds to NCA-160 and NCA-90, whereas CD67 only recognizes NCA-95. As we have shown previously, NCA-160 and NCA-90 present sialylated Lewis-X oligosaccharide Ag (SLex) in a functional way, i.e., these Ag function as (one of many possible) molecules involved in neutrophil binding to the adhesion molecule E-selectin expressed on activated endothelial cells. In this study, we found that a polyclonal anti-CEA antiserum, either as intact Ig or as F(ab')2 fragments, induced neutrophil aggregation. This aggregation response was blocked by CD18 mAb. Neutrophils from a patient severely affected by paroxysmal nocturnal hemoglobinuria completely lacked expression of NCA-95 and NCA-90. The patient's neutrophils repeatedly showed no aggregation on addition of the anti-CEA antiserum. Thus, the presence of the phosphatidylinositol-linked NCA-95/90 seems to be essential for NCA-induced neutrophil activation. Our data indicate that NCA molecules on neutrophils may function via binding to E-selection or an as yet unknown ligand (as mimicked here by an antiserum) and subsequently induce CD18-dependent adhesive properties.