Due to the pulsatile pituitary hormone secretion, their involvement in the acute stress response and feed-back with peripheral hormones, baseline pituitary hormone levels may overlap among normal and pathological subjects. Therefore, dynamic testing has been widely used for the diagnosis and follow-up of pituitary diseases. An ideal test should be sensitive, specific, well tolerated, easy to be standardized and performed and cost-effective. Emerging issues are cost and widespread availability of ultrasensitive hormone assays, increased knowledge of the pathophysiological and pharmacological mechanisms regulating pituitary function and need for better discrimination between clinically useful tests and research tools. In this special issue experts from US and Europe practically approached testing in specific pituitary diseases in the context of current guidelines. Drug effects on different axes are discussed since pharmacologic treatments may influence testing outcome.