1) This is a report of nine patients with agenesis of the corpus callosum. Three of them had a complete defect of the corpus callosum as seen on X-rays; in 4 patients there was a partial agenesis and two patients partial defect was combined with a lipoma. Most of these patients were epileptics. 2) In order to determine the interhemispheric transfer of somaesthetic patterns bimanual tests (comparison of lengths and weights and a maze test) were used. The test results obtained by the acallosal patients have been compared with those of two groups of control persons, one group of normal subjects and a second group of epileptics. 3) A slight impairment of interhemispheric transmission of somaesthetic patterns has been found in the weight test and in the maze test. In part of the tests these results could be established statistically. 4) With comparisons against the control groups the disturbances of the interhemispheric transfer in acallosal patients were more obvious with the more difficult and complex perceptuomotor tasks. 5) In testing the reactions to hemioptic informations we found no hints for special disturbances of interhemispheric transmission in the acallosal patients. 6) On the Hamburg-Wechsler intelligence scale the mean IQ of the nine patients was slightly below average. 7) The test results are discussed in regard to findings after split brain operations in humans and animals.