Oxidative stress is involved in many acute and chronic diseases including cancer, cardiovascular disorders and neurodegenerative diseases. We studied the relationship between the level of intracellular reactive oxygen species in peripheral granulocytes and the estimated anxiety level of mice using the behavioral light/dark choice test. Our results indicate a linear and significant relationship between the intracellular redox status of peripheral blood granulocytes and different parameters of anxiety-related behavior including latency time (R(2)=0.737, P<0.001), cumulative time spent in the lit box (R(2)=0.612, P<0.01) and number of entries into the lit box (R(2)=0.661, P<0.01). These results suggest a positive relationship between peripheral oxidative status and level of anxiety in mice.