Twenty-five undergraduates and university staff (15 females, 10 males) volunteered to take part in a study examining the effects of a short-term mental stressor on the activation of neutrophils in peripheral blood, as determined by the oxidative capacity to reduced Nitro-blue Tetrazolium (NBT). Participants were assigned to one of two groups, an experimental group (n=17) and a control group (n=8). Subjects in the experimental group were subjected to a time-constrained mental stressor and finger-stick blood samples were taken on four occasions. Those in the control group did not complete a stressor task and only experienced the four finger-stick blood samples. Heart rate was recorded at 5-min intervals as a general indicator of arousal. Examination of the stained blood samples showed that a short-term stressor resulted in significant increased activation of neutrophils, which returned almost to baseline levels on completion of the experiment. In contrast, the control group's neutrophils showed no significant change in activation throughout. The results support the hypothesis that short-term, acute stressors may activate neutrophils.