Venous occlusion plethysmography has been used for over a century and is still a powerful tool for recording limb blood flow. It has been used to investigate autonomic regulation, vasodilator responses to exercise, ischemia, emotional stress and changes in body temperature, and to follow changes in endothelium-dependent responses in a number of diseases. Comparisons made between the older, air-filled plethysmographs and the more modern mercury/indium-gallium in silastic strain gauges have indicated that the estimates made of limb blood flow are very similar (see Joyner et al, 2001). Recently, automated rapid inflation systems have been introduced to inflate the sphygmomanometer cuffs that are used to occlude the venous drainage, replacing the use of manual inflation. To our knowledge, there have been no direct comparisons between the blood flow measurements made with automated and manual inflation. In an initial study on 7 male subjects (18-25 years old), forearm blood flow (FBF) was recorded by venous occlusion plethysmography, by using an automated system (E20, Rapid Cuff inflator, Hochansen Inc, USA) that inflated the cuff around the upper arm to 50mmHg. FBF was 8.4±1.1 at rest, 61.2±8.1 ml.min-1.100ml-1 immediately after 3 minutes static contraction at 60% maximum voluntary contraction (MVC) and 53.4±6.1, 45.4±7.9, 35.3±8.2, 29.8±5.4, and 20.9±3.3 ml.min-1.100ml-1 at 30s, 1, 3, 5 and 7 min respectively after contraction: FBF increased at maximum by ~7-fold. By contrast, we previously reported that in a similar group of subjects, FBF increased from 6.8±0.6 ml.min-1.100ml-1at rest, by only ~3.2 fold after static contraction at 60%MVC (Win & Marshall, 2005), suggesting the responses were much larger when recorded with automated inflation. Thus, in a separate study on 5 subjects (3F/2M; 20-30 years old), direct comparisons were made between automatic and manual cuff inflation before and following static contraction at 70% MVC for 1min. With automated inflation, FBF was 7.2±0.6 ml.min-1.100ml-1 at rest and 44.4±6.8 ml.min-1.100ml-1 immediately after, and 32.9±4.7, 26.8±3.4, 21.5±3.4, 16.9±2.9,11.6±3.4 ml.min-1.100ml-1 at 30s, 1, 3, 5 and 7 min respectively after contraction, whereas with manual inflation the corresponding values were 8.2±2.2 at rest and 32.8±5.5, 20.3±1.7, 17.8±2.7, 14.6±2.8,12.4±2.4 and 9.6±2.6 ml.min-1.100ml-1. These values were significantly different from 0-3min after contraction (P<0.05, repeated measures ANOVA). Venous occlusion plethysmography underestimates limb blood flow relative to the thermodilution technique (Joyner et al, 2001). The present results indicate that automated cuff inflation gives a better estimation than manual inflation; this would have tremendous implications for use of the technique in physiological and clinical studies.