Right handedness is one of the most prominent markers of human functional brain asymmetry. Deviation from this norm appears to be associated with certain developmental disorders. While many studies have dealt with the genetic contribution to the determination of handedness, few have examined whether environmental factors that are subtler than forced hand switching can modulate the development of handedness. In this study, we exposed rats to a novel environment for 3 min daily during their first 3 weeks of life and found that their paw preferences during both infancy and adulthood showed a leftward shift compared with the controls. This result suggests that 'handedness' can be modified by rather subtle early environmental manipulation. Since exposure to a novel environment does not involve a direct asymmetric activation of the sensory--motor system underlying paw-use, mechanisms beyond this paw-specific system must exist to mediate the observed modulation of 'handedness'.