It has been previously demonstrated that warning stimuli (WS) reduce reaction time (RT) by causing cortical activation. The purpose of this study was to use verbal and non-verbal WS to see if these stimuli asymmetrically activate the cerebral hemispheres. Sixteen right-handed Ss were given a manual RT task using a light as the RT stimulus and either verbal or non-verbal sounds as WS. RTs by the right hand were significantly faster with verbal WS than with non-verbal WS. There were no significant differences for the left hand between the verbal and non-verbal WS. These results give partial support to the asymmetrical activation hypothesis. © 1976.