Measurement of the oxygenation of the peripheral tissues provides useful information about tissue perfusion. A method is described for the measurement of peripheral venous oxyhaemaglobin saturation (SvO2) in the adult forearm by a noninvasive technique, near infrared spectroscopy (NIRS) with venous occlusion. A series of studies is performed on healthy adults to compare measurements of forearm SvO2 made by NIRS with measurements of superficial venous SvO2 made by co-oximetry, and to study the effect of different optode spacings. There is a significant correlation between forearm SvO2 measured by NIRS and SvO2 of superficial venous blood measured by co-oximetry (n = 19, r = 0.7, p < 0.0001). Higher values for SvO2 were obtained using a 2.5 cm spacing than with a 4 cm spacing (mean difference = 4.1% (95% CI 1.4%-6.8%) n = 16). This difference is likely to have been due to a more superficial volume of tissue being studied with the closer optode spacing. Peripheral SvO2 can be measured non-invasively using NIRS with venous occlusion. It may prove to be a useful method to study circulatory disturbances.