Over the last few decades, several delayed-start trials have suggested that early introduction of dopamine replacement therapy can improve the prognosis of Parkinson\'s disease (PD). Moreover, several observations support that L-dopa is non toxic to normal and diseased substantia nigra in humans. Thus, the clinical practice guideline 2018 for PD recommends L-dopa as an initial treatment for PD, in principle. More recently, several potential disease-modifying therapies have been reported to be effective. Furthermore, several recent studies suggest that exercise can be beneficial in delaying disease progression.

Available evidence on the practice of acute pharmacological challenge tests in parkinsonian patients was reviewed by a committee of experts, which achieved a general consensus. The published data deal mainly with the acute administration of levodopa and apomorphine in Parkinson\'s disease. Such challenge may serve different purposes, e.g., research, diagnosis, or tailoring of treatment. Unique protocols describing the clinical setting and practice parameters are not available. The present paper describes the scientific background and supplies practical guidelines, whenever possible, to perform and evaluate acute challenge tests in parkinsonian syndromes. With the appropriate indication and setting, acute challenge tests are useful in diagnosis and therapy of Parkinson\'s disease and related disorders.