Reactive oxygen species (ROS) produced by neutrophils are essential in the host defense against infections but may be harmful to neutrophils themselves. Glutathione (GSH) plays a pivotal role in protecting cells against ROS-mediated oxidant injury. Cystine/glutamate transporter, designated as system x(c)(-) and consisting of two proteins, xCT and 4F2hc, is important to maintain GSH levels in mammalian-cultured cells. In the present paper, we have investigated system x(c)(-) in neutrophils. In human peripheral blood neutrophils, neither the activity of system x(c)(-) nor xCT mRNA was detected. The activity was induced, and xCT mRNA was expressed when they were cultured in vitro. The mRNA expression was much enhanced in the presence of opsonized zymosan or PMA. In contrast, mouse peritoneal exudate neutrophils, immediately after preparation, exhibited system x(c)(-) activity and expressed xCT mRNA. The activity and the expression were heightened further when they were cultured. Peritoneal exudate cells (mostly neutrophils) from xCT-deficient (xCT(-/-)) mice had lower cysteine content than those from the wild-type mice. GSH levels in the xCT(-/-) cells decreased rapidly when they were cultured, whereas those in the wild-type cells were maintained during the culture. Apoptosis induced in culture was enhanced in the xCT(-/-) cells compared with the wild-type cells. These results suggest that system x(c)(-) plays an important role in neutrophils when they are activated, and their GSH consumption is accelerated.