36 Ss worked approximately 23 min. on the pursuit rotor. Ss practiced in pairs in alternation. Half practiced a 50-sec. work, 60-sec. rest cycle, and half a 5-min. work, 6-min. rest cycle. It appeared that little or no conditioned inhibition developed during massed practice. A comparison made of the scores of the "successful" versus those of the "unsuccessful" members of the pairs in the massed practice group shows the latter to gain more over rest periods. This can be interpreted in the following terms: the poorer performers were more motivated, hence tolerated more reactive inhibition during practice; this was dissipated over rest and hence led to greater gain (PsycINFO Database Record (c) 2006 APA, all rights reserved)