This study asked whether lexical availability affects the length, complexity, order of mention, and fluency of children's utterances. Lexical availability was manipulated through discourse support (present or absent) and word frequency (high or low) for 40 target nouns. Length was indexed by mean number of words per communication unit. Complexity was indexed by mean number of verbs per communication unit. Earlier mention was measured by mean number of words preceding the target word in each communication unit. Thirty-six subjects, aged 4, 6, and 8, described 40 illustrations containing a high or low frequency target noun referent. In the discourse support condition, provided for one half of the target words, subjects named the target word prior to the description task. Results showed that the number of responses containing the target word varied with age, word frequency and discourse support condition; length of responses varied with age and its interaction with discourse support; earlier mention varied with age and discourse support condition; and fluency varied with discourse support condition. The results are discussed from the viewpoint of Bock's process model of sentence production.