Oral glucose administration increased plasma noradrenaline concentration significantly in seven normal subjects (p<0.02), whereas in six young short-term Type 1 diabetic patients without complications plasma noradrenaline did not change. Basal plasma noradrenaline did not differ between the two groups. In the first 3 h after oral glucose administration, the mean heart rate in eight normal subjects was increased 3.5% above basal levels (p<0.05). In contrast, no such increase was found in eight Type 1 diabetic patients after glucose administration. In two normal subjects thoroughly examined before and after oral glucose administration, we observed a significant correlation between heart rate and systolic blood pressure (p<0.001) but this was not seen in two diabetic patients in whom neither heart rate nor systolic blood pressure increased. Our findings indicate that sympathetic nervous activity and cardiovascular function is abnormal in early diabetes during an oral glucose load.