We studied the effects of a single retrobulbar injection of Botulinum toxin on the motility of cat eyes. Four cats were sedated and the opposite eye served as a control. Eye movements were plotted by reflecting a laser beam from a mirror fixed to the cornea. We found the mean degrees of deviation per eye per day and summarized these results as mean degrees of deviation per eye per week +/- standard deviation. Statistical analysis was accomplished using Student's t test for independent measures, since measurement of the treated eye pairs was done in a randomized manner on different test days. (table; see text) These results indicate that a single retrobulbar dose of Botulinum toxin can produce a paralysis of the ocular musculature lasting in excess of four weeks in a specific and reproducible manner. In addition, this methodology should prove useful in future experiments in which ocular motility might prove to be a technical concern.