AbstractIt is recognized that residual pancreatic /3‐cell function may play a role in the control of blood glucose in patients with insulin‐dependent diabetes mellitus (IDDM). Since modern therapy is concerned with the possibility of recovery of pancreatic β‐cell function, we need to identify the secretagogue of choice in the various phases of IDDM.Eleven patients with IDDM underwent four different stimulation tests of (3‐cell function over two weeks. The tests were i.v. arginine (ATT), oral glucose (o‐GTT), i.v. glucagon (GCT) and i.v. tolubutamide (TTT). One patient had the tests repeated four times over two years after the onset.Among the tests, ATT and o‐GTT produced the largest response ofC‐peptide. The response to GCT was small in comparison. TTT had no significant effect. The present study suggests that ATT or o‐GTT or both are useful in the evaluation of endogenous insulin secretion during follow‐up of IDDM. On the other hand, GCT can only be used as a simple screening method for residual ß‐cell function and is not sufficient for quantitativ