A group of preschool-aged children with specific language impairment (SLI), a group of typically developing children matched for age (TD-A), and a group of younger typically developing children matched for mean length of utterance (TD-MLU) were presented with novel verbs in contexts that required them to inflect with past tense "-ed." The novel verbs differed in their phonotactic probabilities. The children with SLI were less likely than the other two groups to produce the novel verbs with "-ed." Furthermore, they were less likely to use "-ed" with novel verbs of low phonotactic probability than those of high probability; this difference was not seen in the other two groups of children. It appears that the phonotactic composition of verbs is one factor that can contribute to the variability of past tense use by children with SLI. (Contains 2 tables.)