This paper will discuss recently obtained physiological and acoustic data related to some theoretical issues surrounding the motor organization of speech rate. The specific question that will be addressed is whether vowel target undershoot, increased articulatory velocity, and greater coarticulation between adjacent segments, features associated with increased speaking rate, can be explained by a simple horizontal time-compression model. This question was explored experimentally in a number of utterances by studying changes in segmental duration and articulatory effort as reflected by changes in the duration and amplitude of the muscle contractions underlying the production of these utterances. The results will also be discussed in terms of general theories of speech motor planning and recent perceptual studies of speech rate. [Work supported by NIH Grant NS-10424 and NSF Grant BSN-7616954.]