During polysomnography, measurement of airflow and respiratory effort are essential for classifying the type of respiratory event and for evaluating the efficacy of treatment. There are various ways to measure respiratory effort, the reference technique being oesophageal manometry. This measures fluctuations in intrathoracic pressure which correspond to variations in upper airway resistance and therefore allows differentiation between central and obstructive respiratory events. Thus the simple snorer can be distinguished from an individual with the upper airway resistance syndrome (UARS). In the UARS abnormally high resistance develops in the upper airway in the absence of identifiable apnoeas and hypopnoeas. The characteristic cresendo-decresendo pattern of the oesophageal pressure signal, when associated with the micro-arousals which are responsible for the hypersomnolence, is pathognomonic of this condition. The clinical application of oesophageal manometry is limited by its poor tolerance in certain individuals and by the potential deleterious effect the catheter itself has on sleep quality and on the dynamics of the upper airway. Other less invasive techniques, such as nasal pressure and pulse transit time, are currently under evaluation.