The effect of a single brain lesion on Reaction Times (RTs) to unpatterned visual stimuli was studied in 20 right brain-damaged (RBD) and 19 left brain-damaged (LBD) patients with single small vascular lesions confined to one hemisphere and free of visual field defects and of significant neuropsychological abnormalities (e.g. aphasia or hemineglect). The stimulus was presented in the field either ipsilateral or contralateral to the brain lesion. The stimulus location was either blocked in each hemifield or randomly alternating between fields. RTs in RBD patients were not statistically different from RTs in LBD patients. Intrahemispheric site of the lesion also was irrelevant for the lengthening in RTs. Responses to blocked presentations were faster than to random presentations. Responses to the hemifield contralateral to the brain lesion were slower than to ipsilateral hemifield, and the difference was unrelated to the absolute values of RTs. It is concluded, in contrast to other reports, but in agreement with the more recent literature, that there is no hemispheric dominance for RTs.