Purpose: This study sought to investigate the interaction of speech movement execution with higher order lexical parameters. The authors examined how lexical characteristics affect speech output in individuals with Parkinson's disease (PD) and healthy control (HC) speakers. Method: Twenty speakers with PD and 12 healthy speakers read sentences with target words that varied in word frequency and neighborhood density. The formant transitions (F2 slopes) of the diphthongs in the target words were compared across lexical categories between PD and HC groups. Results: Both groups of speakers produced steeper F2 slopes for the diphthongs in less frequent words and words from sparse neighborhoods. The magnitude of the increase in F2 slopes was significantly less in the PD than HC group. The lexical effect on the F2 slope differed among the diphthongs and between the 2 groups. Conclusions: PD and healthy speakers varied their acoustic output on the basis of word frequency and neighborhood density. F2 slope variations can be traced to higher level lexical differences. This lexical effect on articulation, however, appears to be constrained by PD.