In order to investigate the pancreatic function in patients with thalassaemia major, plasma glucose and immunoreactive C-peptide levels were determined in 9 diabetic thalassaemic patients and in 7 controls after arginine infusion. Mean basal and peak values and C-peptide areas in thalassaemic patients did not differ significantly from those of the controls. However, in the thalassaemic group there was a greater variation in values, since pancreatic beta-cell function was found either normal, reduced or increased. These findings could suggest that different factors may lead to diabetes which complicates thalassaemia, i.e. insulin-resistance, probably due to liver damage subsequent to iron deposition and infectious hepatitis, and insulinopenia, probably due to beta-cell lesion following iron storage in the pancreas.