Twelve patients with idiopathic Parkinson's disease had acoustic speech analysis of sentence utterances to provide information on speech tempo and accuracy of articulation. As a measure of rate of speech the duration of opening-closing movements during articulation was determined from speech wave variables. The intensity of sound emission during articulatory closure as required for stop consonant production, for example, magnitude of p, magnitude of t, magnitude of k, was used as an index of the degree of closure. Speech tempo was not significantly different from normal. The patients, however, had a reduced capacity of completing articulatory occlusion. This was interpreted as reflecting a reduction in movement amplitude of the articulators. Articulatory "undershoot" was not uniform but influenced by linguistic demands in that the closures associated with a stressed syllable were performed at the expense of unstressed ones. Furthermore, switching between opening and closing movements of the articulators in sentence production seemed undisturbed. These results indicate that motor planning of speech differs from arm movement control.