Two experiments are reported testing the adequacy of Hull's constructs of I-sub(R) and -sub(S)I-sub(R) as basis of explanation for alternation behavior in the rat. The designs systematically controlled or varied (1) amount of bar weight, (2) length of inter-trial interval, and (3) number of trials, in a single unit Y-maze with bar levers in each goal-arm. The results indicate that only (2) and (3) above affect per cent of alternation, this the author points out is not in agreement with predictions based on Hull's ninth postulate. An alternative explanation of "exploratory tendency" is offered. (PsycINFO Database Record (c) 2006 APA, all rights reserved)