The lateralized functional differentiation between the right and the left cerebral hemispheres is called cerebral lateralization. To date the language function has been supposed to be lateralized in the left hemisphere and the visuospatial function to be lateralized in the right in the typical differentiation for right-handed subjects.     Since there has recently been an increasing number of reports on cases of imperfect lateralization from the viewpoint of the language function, we discussed this point in terms of the visuo-spatial function in 100 cases of putaminal hemorrhage (50 cases with right lesion, 50 with left).     Unilateral spatial neglect (U. S. N.) was noted in 29 (58 %) out of 50 cases with the right-sided lesion, and it continued for more than 2 months in 18 of these cases (60 %). On the other hand U. S. N. was noted in 5 cases (10 %) out of 50 with the left lesion, but it disappeared in 3 of these cases within 1 month. These 5 cases were either left-handed, ambidextrous or had the familial disposition of left-handedness.     The above results suggested the possibility of imperfect lateralization in the cases of U. S. N. with the left-sided lesion.