A portable device (the Diabalert), which measures the electrical conductivity of the skin surface and sounds an alarm at a preset conductivity, was evaluated as a possible detector of hypoglycemia-induced sweating in diabetic subjects. Insulin was infused intravenously into seven insulin-dependent diabetic subjects, and the course of the plasma glucose decline, hypoglycemic symptoms, and state of consciousness of the patients frequently monitored. In five patients sweating occurred with hypoglycemia, and the Diabalert alarm was activated at plasma glucose concentrations between 1.6 and 3.7 mmol/L. Three of these five diabetic patients were by then unaware of the alarm and would have failed to take corrective action to restore normoglycemia. Two further patients had virtually no symptoms despite marked biochemical hypoglycemia and the alarm was not triggered. Studies are needed in larger numbers of diabetic patients at home to fully assess the clinical usefulness of this device.