The influence of human monocyte-derived chemotactic peptide (GCP/IL-8) on degranulation of neutrophils was investigated in relation to that of other monokines. GCP/IL-8 promoted a dose-dependent release of lactoferrin from specific granules but had no effect on enzyme release from primary granules. From the other monokines that were tested, tumour necrosis factor alpha (TNF alpha) also induced degranulation, while IL-1 beta and IL-6 scored negatively. TNF alpha-induced lactoferrin release was enhanced by cytochalasin B pretreatment of the granulocytes, while GCP/IL-8-promoted degranulation was not. In contrast to GCP, TNF alpha also caused the release of LDH, suggesting a non-specific cell destruction. These observations further support the view that, unlike the other monokines, GCP/IL-8 is a true and specific granulocyte activator.