Neutrophil apoptosis is a constitutive process that can be enhanced or delayed by various stimuli. In this study, effect of brefeldin A (BFA), which affects biological process of secretion, on constitutive and delayed apoptosis of neutrophils was investigated. Neutrophil apoptosis was determined after culturing for 20 hr in vitro by morphological changes, annexin V staining and DNA electrophoresis. BFA increased the constitutive apoptotic rate of neutrophils in dose-dependent manner. The delay of apoptosis induced by granulocyte macrophage-colony stimulating factor and lipopolysaccharide was also blocked by 10 $mu$M of BFA. However, this effect of BFA was less marked when neutrophils were treated with dexamethasone, interleukin-8, or dibutyryl-cAMP. Moreover, the delay of neutrophil apoptosis induced by rottlerin, a specific inhibitor of protein kinase C-$delta$ was significantly abrogated by BFA. Although BFA-induced apoptosis was not blocked by the caspase-3 inhibitor, zDEVD-fmk, expression levels of myeloid cell leukemia-1 (Mcl-1) were down-regulated by BFA. These results suggest that derangement of vesicular protein transport may be involved in the apoptosis of neutrophils, and that the action of BFA on apoptosis is dependent on changes in the expression of Mcl-1.