Barognosis was tested in a patient who had a lesion of the right cerebellar hemisphere. While blindfolded, he used each hand to estimate the mass of given test loads, alternating hands between trials. He moved each load sinusoidally, comparing it with the previous one. The period of oscillation was found to be a linear function of the mass. With each load, the period of oscillation was longer when he used the ataxic hand. On 23 of 59 comparisons between loads, the patient reported incorrectly. Ninety-one percent of the errors were in the direction of loads feeling heavier when the ataxic hand was used. To explain these results, it is proposed that (1) the perceived magnitude of a load depends on the corollary discharge, and (2) cerebellar damage may reduce the accuracy of the corollary discharge.