Twelve monkeys, 3 unoperated control animals and 9 with division of various cerebral commissures, were trained on a tactile discrimination task before surgery and retrained post-operatively on the same task with the hand used during original learning. After surgery, the 6 animals with section of the posterior commissural region showed impaired performance on the task learnt pre-operatively, whereas 6 monkeys not having this section were unimpaired. The evaluation of the results points to a non-specific mechanism involved.