In order to achieve fluid balance, the mean capillary pressure must be equal and opposite to the membrane osmotic pressure (MOP) across the capillary membrane. Capillary pressure is difficult to measure but mean arterial pressure (MAP) can be used as a surrogate 1,4 . If fluid balance is achieved when MAP = MOP then four imbalance situations can be envisaged; high MAP + low MOP, high MAP +high MOP, low MAP + low MOP and low MAP + high MAP. These correspond to oedema, hypertension and high and low osmotic pressure shock (Fig1). The MAP’s and MOP10K’s of 30 healthy volunteers 1,4 fell within the “normal area”. The outliers to the right had consumed party volumes of alcohol the night before the study! Thirty five patients with clinical oedema 1,2 had high MAP’s and low MOP10K’s. The MAP and MOP10K’s of 22 hypertension patients fell into the raised MAP and MOP sector 1,2. Our most recent study of 57 patients admitted with shock, 23 had low (<24mmHg), 17 had normal (24-27mmHg) and 13 had high MOP’s. These results are shown graphically in Fig 2. These studies give growing support to the concept that oedema, hypertension and shock are osmotic diseases resulting from imbalances between MAP and MOP10K