To determine whether incomplete reward reduction and reward increment would influence the "frustration effect" (FE) in double alleyway, rats were given 153 trials with 50% partial reward in Goalbox 1 with 4 or 12 pellets in Goalbox 1 and 4 or 12 pellets in Goalbox 2. On trials 106-153, the postshift phase, half of the rats in each group were shifted to a reward magnitude opposite to that previously received in Goalbox 1. During preshift, Alley 1 start and running speeds were inversely related to Goalbox 2 reward magnitude. The size of the FE was directly related to Goalbox 1 and Goalbox 2 reward magnitude. During postshift, Alley 1 running were inversely related to preshift Goalbox 1 reward magnitude. The size of the FE was directly related to Goalbox 1 and Goalbox 2 reward magnitude. The results were discussed in terms of Amsel's theory of frustration. / Master of Science