Highly purified human interferon-gamma (IFN-gamma) induced a respiratory burst and lysosomal enzyme release in human neutrophils. The lymphokine augmented the respiratory burst induced by phorbol myristate acetate (PMA), or N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP), and increased the release of specific granule enzymes induced by opsonized zymosan. Viability and locomotion of neutrophils were unaffected by IFN-gamma.