Opposing views of storage and processing of morphologically complex words (e.g., past tense) have been suggested: the dual system, whereby regular forms are not in the lexicon but are generated by rule, while irregular forms are explicitly represented; the single system, whereby regular and irregular forms are computed by a single system, using associative connections; and a system whereby phonological rules relate both regular and irregular past to present tense forms. Two reaction time experiments investigated the production of the past tense in English in response to the auditory presentation of the present tense of the verb. The first experiment addressed the methodology of presenting regulars and irregulars in blocked form as in a previous study (Jaeger et al. in Language 72:451-497, 1996). Blocked presentation results showed longer RTs for the elicitation of irregular pasts than for regular pasts; however, there were no differences between regular and irregular elicitation when the presentation was randomized, indicating that it is rules that are being primed. The second experiment tested whether the response time advantage found for blocked regular verbs in the first experiment might also extend to irregular verb forms exhibiting the same sub-regularity (e.g., sing-sang may prime ring-rang). Results showed a trend towards slower RTs when past tense forms from different sub-regularities follow one another, suggesting interference between one sub-regularity and another.