The correlation between nitric oxide (NO) levels in the cortices and brain lateralization was investigated via the paw preference test in which three groups of mice (left-pawed, ambidextrous and right pawed) were selected. Results showed that the right cortices had higher NO levels than the left cortices for both normal and lipopolysaccharide-treated mice. There were significant differences in NO levels in the right/left cortices depending on the behavioral lateralization as expressed by paw preference. Finally, individual levels of NO in the right/left cortices correlated well with individual paw preference scores. The relationship was parabolic. The results suggest a strong relationship between NO asymmetries as well as the direction and the intensity of behavioral lateralization.