Measurements of the glucose concentration in venous blood and parotid saliva taken from 31 diabetics attending a diabetic clinic showed values ranging respectively from 3.9 to 19.1 mmol/l and 0.06 to 0.83 mmol/l (means 9.6 mmol/l and 0.32 mmol/l respectively). Linear regression of salivary glucose on blood glucose gave a simple correlation coefficient of 0.18 (NS). Since salivary glucose levels did not reflect blood glucose levels, the possibility of diabetics regulating their metabolic control by the noninvasive technique of monitoring salivary glucose concentrations is not possible.