Speech pathologists often describe voice quality in hypokinetic dysarthria or Parkinsonism as harsh or breathy, which has been largely attributed to incomplete closure of vocal folds. Exploiting its harmonic nature, we separate voiced portion of the speech to obtain an objective estimate of this quality. The utility of the proposed approach was evaluated on predicting 116 clinical ratings of Parkinson's disease on 82 subjects. Our results show that the information extracted from speech, elicited through 3 tasks, can predict the motor subscore (range 0 to 108) of the clinical measure, the Unified Parkinson's Disease Rating Scale, within a mean absolute error of 5.7 and a standard deviation of about 2.0. While still preliminary, our results are significant and demonstrate that the proposed computational approach has promising real-world applications such as in home-based assessment or in telemonitoring of Parkinson's disease.