Although a variety of medications are used in the treatment of Parkinson's disease, all have short term effects. As a result, motor performance varies over time. A key role of the physiotherapist is to measure fluctuations in the severity of movement disorders in relation to the dose and timing of anti-Parkinsonian medication with a view to: (i) optimising motor performance; (ii) targeting therapeutic interventions for times of greatest need; and (iii) communicating findings to the inter-professional team. For an informed approach to the measurement of medication-induced motor fluctuations, clinicians require an understanding of the pathophysiology of Parkinson's disease, the mode of action of medications and the validity of existing methods used to quantify changes in performance resulting from pharmaceuticals and rehabilitation.