The comparative effects of intranasal and subcutaneous insulin on blood glucose and insulin levels are described in non-obese type II diabetics, in the fasting state and following a standard meal. In the fasting studies, intranasal insulin (30 units) produced a single early insulin peak. Elevated insulin levels and their hypoglycaemic effect persisted for less than 2 h whereas with subcutaneous insulin (8 units) elevated insulin levels and evidence of hypoglycaemic action were still present at 4 h. By contrast, in the meal studies both forms of insulin had similar effects on serum insulin levels and blood glucose. Moreover elevated insulin levels and evidence of reduction in post-prandial hyperglycaemia were now present at 4 h with both intranasal and subcutaneous insulin administration. Intranasal insulin in combination with a test meal now produced a biphasic insulin profile more closely resembling the normal insulin response to a meal, and reflecting the combined effects of endogenous and exogenous insulin.