The performance of untreated naive mice on the usual constantly rotating rotarod is so variable that preliminary training (to eliminate very low readings) and the introduction of a time limit for any one trial (to eliminate very high readings) are necessary to obtain statistically significant measures of performance. Such procedures are however undesirable since a) drugs might conceivably affect memory rather than motor coordination in trained mice and b) the artificial time limi~ reduces the sensitivity of the procedure. The prototype apparatus demonstrated is a constantly accelerating rod that eliminates the problems outlined above.~ iiee are placed on a stationary rod which then slowly and linearly accelerates so that even the most agile mouse is unable to stay on the rod for more than a few minutes. Preliminary results obtained with this apparatus indicate that the mean performance of groups of 25 naive mice is very constant and that the standard errors are small. The effects of standard centrally active drugs on motor coordination are also detectable at lower dose levels than on~ he more usual type of rotarod and can be quantitatively measured.