A variable model of venous hypertension was used to examine the immediate effect on skin oxygenation and blood flow. Measurements were carried out using laser Doppler flowmetry, transcutaneous oximetry and both macro- and micro-lightguide spectrophotometry to measure haemoglobin saturation (SO2). Assessments were performed on 20 normal subjects and in ten patients with deep venous insufficiency lying supine with a pressure cuff left uninflated (P0), then inflated to 40 mmHg (P40), 60 mmHg (P60) and 80 mmHg (P80). All measurements were performed at the gaiter area of the leg. In normal subjects median Doppler values fell significantly at P40 (P <0.001) but further pressure increases had no more effect. Mean values of transcutaneous partial pressure of oxygen (PtcO2) fell steadily (P <0.001), although the initial fall at P40 was small. Median SO2 fell with increasing occlusion pressure with both macro- and micro-lightguide spectrophotometry (P <0.001), although the main reduction occurred predominantly at lower occlusion pressures. Higher levels of SO2 were obtained with local heating up to 44 degrees C, with a pattern similar to that of PtcO2. In patients, the same pattern of response to increased venous pressure occurred in areas of clinically normal skin. These data suggest that small increases in venous hypertension have an immediate and profound influence on skin blood flow and oxygen availability in normal skin.