For the monitoring of arterial blood pressure in the peri-operative period, three different methods are available. The classical approach is the indirect measurement employing a cuff applied to the upper arm as described by RIVA-ROCCI, known as sphygmomanometry. Thanks to the development of automatic devices employing the oscillometric principle, measurement of the mean arterial pressure has now become possible, blood pressure monitoring simplified, and documentation made easy. The particular indications for direct arterial pressure measurement are very low, very high, and widely fluctuating pressure, as well as major and prolonged surgery. Furthermore, arterial catheterisation provides the additional advantage of permitting blood gas analysis, while, properly employed, the rate of associated complications is low. Recently, it has become possible to perform continuous recording of the blood pressure with a non-invasive method known as servo-plethysmomanometry. The device employed for this method (Finapres) measures the pressure in the arteries of a finger using a small cuff incorporating a photoplethysmograph. Experience to date with this method in clinical usage is good. It is thus to be expected that the technique will in future offer an alternative to invasive methods of blood pressure measurement in many cases.