This paper presents results of an acoustic investigation of speech in progressive supranuclear palsy (PSP), multiple system atrophy (MSA) and idiopathic Parkinson's disease (IPD). The study had two aims: (a) to provide a first acoustic description of the speech of people with PSP and MSA, (b) to compare acoustic characteristics of the dysarthria associated with PSP and MSA with classic hypokinetic dysarthria. Four acoustic parameters (voice quality, pitch range, vowel space and rate in syllable repetition) were investigated in 17 patients with PSP and 9 patients with MSA and compared with data from a large-scale study of IPD patients. Participants with PSP and MSA performed significantly worse than the PD group on Alternating Motion Rate tasks. In addition, the pitch range of PSP participants was restricted. We discuss the potential of these speech tasks for early differential diagnosis.