Abstract Rhesus monkeys tend to use a particular hand more frequently whenever it is the one nearer to the object to be grasped. This bias, due to body position relative to the object, can be eliminated by determining separately the percentage of reaches with one hand when the animal is on each side of the object to be grasped and then averaging the results from both sides. The prevention of stereotyped repetitive reaching may also be important in obtaining a more accurate estimate of hand performance. When these factors were taken into account in a study of 24 monkeys, all degrees of hand preference, both strong and weak, occurred with equal frequency. This contrasts with previous studies in which a majority of the animals had marked right- and left-hand preferences and only a minority were relatively ambilateral. The relevance of these findings to the phenomenon of handedness and cerebral dominance in man is discussed. Individual monkeys show a consistent preference for the same hand from one test session to the next. This suggests a possible contralateral cerebral hemispheric motor predominance. When the optic tract contralateral to the preferred hand was sectioned there was some tendency to continue the same hand preference. This occurred despite the lack of direct visual input into the cerebral hemisphere contralateral to the preferred hand. However, if the posterior half of the corpus callosum was also divided, hand preference changed almost completely to the previously non-preferred hand. In effect, provided the interhemispheric connections between the sensory association areas are intact, the predominant hemisphere can usurp the use of visual information presented to the other hemisphere. These observations can most easily be interpreted by assuming that contralateral cerebral hemispheric predominance is not only a motor but also a sensory phenomenon.