The current study presents preliminary data regarding the development and validation of a rating system designed to classify PD patients into clinical subgroups. Using portions of the Unified Parkinson's Disease Rating Scale, a ratio value was derived, yielding three patient subtypes: a tremor-dominant group (T), an akinetic-rigid group (AR), and a mixed group (MX). Validation of the schema was conducted by grouping PD surgical candidates into specific disease subtypes and evaluating differences in neurotransmitter profiles among disease subtypes and non-PD neurological controls. High pressure liquid chromatography analysis of ventricular cerebrospinal fluid indicated 5-hydroxyindoleacetic acid was significantly lower in the AR and MX groups compared to non-PD controls; whereas, glycine was significantly higher in the AR group compared to the T, MX, and control groups. The results suggest that an operational approach can be utilized to differentiate between PD subtypes with distinct neurochemical profiles.