The study of absolute defects of the visual fields, such as the homonymous hemianopias, has long engaged the attention of investigators. However, those partial homonymous defects called hemiachromatopsia (color blindness in one-half the visual field) and hemiamblyopia (impairment of visual power in one-half the visual field) have been studied infrequently and for the most part inadequately. In the routine preoperative study of 24 epileptic patients in whom the corpus callosum was surgically sectioned by Dr. W. P. Van Wagenen (Van Wagenen and Herren1), 3 were found for whom the results of routine perimetric studies were normal but who showed a disturbance in the recognition of colors, objects and letters in one homonymous field. The present paper deals with the cases of these 3 patients. The present study is reported for two reasons. It is concerned, first, with the possible value of such a defect in the diagnosis of focal