Tested the implicit-associative response (IAR) hypothesis of frequency theory in verbal discrimination (VD) learning by varying the number of taxonomic categories used to make up lists. 6 different groups of 20 undergraduates learned to criterion 12-pair lists which varied the number of pairs (1-6) and number of categories (2-12). Results support the hypothesis that, in general, the more pairs that belong to the same taxonomic category, the more difficult it is for Ss to master the list. Results are interpreted as evidence that multiple instances of the same associative arrangement may be necessary to demonstrate consistent IAR effects in VD learning. (PsycINFO Database Record (c) 2006 APA, all rights reserved)