The NB1 glycoprotein (CD177, HNA‐2a antigen) is exclusively expressed on human neutrophils. As the clinical significance of CD177 expression is unknown, we investigated its expression in healthy individuals before and after stimulation with granulocyte colony‐stimulating factor (G‐CSF), in patients with rheumatoid arthritis, viral hepatitis, severe bacterial infections and polycythaemia vera. Expression was quantitatively determined by flow cytometry and by real time polymerase chain reaction. Only G‐CSF‐stimulated individuals and patients with severe bacterial infections and polycythaemia showed a significantly (P < 0·001) increased CD177 expression compared with healthy individuals, indicating that neutrophil CD177 expression can increase significantly in certain clinical conditions.