The present study focuses on the relation between a grammatical and a lexical-semantic aspect of verb production. The spontaneous speech of three different populations (normally developing children, agrammatic aphasics, and children with a specific language impairment) has been analyzed with respect to the proportion of finite clauses and the diversity of the produced lexical verbs. The group results show that in the three populations both the proportion of finite verbs and the variability of the lexical verbs is low. When the individual scores are considered, differences between the normally developing children and the language-impaired subjects show up. Whereas in normally developing children verb finiteness and verb variability go hand-in-hand, the reverse relationship between these variables is observed in the agrammatic aphasics and the children with a specific language impairment. Given this reverse relationship, it is probable to assume two separate disorders. We therefore suggest an impairment at the interface level where lexical information and syntactic structure are integrated during sentence production.