Models of the mental representation of morphologically complex words traditionally fall into one of two categories, Single-Route or Dual-Route models. The former further distinguish between Full-Listing (e.g. Butterworth, 1983) and Decomposition (e.g. Taft & Forster, 1976), while the latter assume different systems governing the access of mono- vs. polymorphemic words (e.g. Pinker & Prince, 1994; Pinker & Ullman, 2002). One of the main arguments against decomposition and continuous online computations is the cognitive resources this process would require. Turning this reasoning around, taxing someone's working memory capacities should then uniquely affect the computation of bimorphemic verb forms. We tested this hypothesis on 48 Dutch native speakers with a lexical decision task, comparing reaction times for Dutch regular past tense forms to frequency-matched irregular past tense forms, both under low and under high cognitive load. We found that frequency influenced reactions to monomorphemic but not to bimorphemic forms (F(1, 47) = 4.734, p = .035), favoring a listing account for the former but a computational procedure for the latter forms. This interaction, however, was present only for a certain group of people (F(1, 23) = 6.279, p = .02), namely those whose reaction times were hardly affected by the load manipulation and who thus may be thought of as having larger working memory capacities. On the other hand, participants who showed a strong load effect had no interaction between number of morphemes and frequency (F(1, 23) = .575, ns), indicating that they process monomorphemic and bimorphemic forms in a similar manner. It seems that cognitive capacities influence the storage of and access to polymorphemic verb forms. While people with greater working memory skills use these resources to compute morphologically complex inflections on-line, people with smaller cognitive capacities seem to rely on a list-like storage for bimorphemic forms as well.