This study presents a series of empirical investigations to test a theory of speech production proposed by Butterworth and Hadar (1989; revised in Hadar & Butterworth, 1997) that iconic gestures have a functional role in lexical retrieval in spontaneous speech. Analysis 1 demonstrated that words which were totally unpredictable (as measured by the Shannon guessing technique) were more likely to occur after pauses than after fluent speech, in line with earlier findings. Analysis 2 demonstrated that iconic gestures were associated with words of lower transitional probability than words not associated with gesture, even when grammatical category was controlled. This therefore provided new supporting evidence for Butterworth and Hadar's claims that gestures' lexical affiliates are indeed unpredictable lexical items. However, Analysis 3 found that iconic gestures were not occasioned by lexical accessing difficulties because although gestures tended to occur with words of significantly lower transitional probability, these lower transitional probability words tended to be uttered quite fluently. Overall, therefore, this study provided little evidence for Butterworth and Hadar's theoretical claim that the main function of the iconic hand gestures that accompany spontaneous speech is to assist in the process of lexical access. Instead, such gestures are reconceptualized in terms of communicative function.