We have compared intraoperative glycaemic control, insulin requirements and metabolic and endocrine variables in 40 non-insulin-dependent diabetic patients (NIDDM) and 40 insulin-dependent diabetic patients (IDDM) undergoing general anaesthesia for elective procedures. Two i.v. insulin regimens were used: continuous i.v. infusion (group A: 1.25 u.h-1) and repeated i.v. boluses (10 u./2 h). Blood concentrations of glucose were measured every 15 min from just before induction of anaesthesia until 2 h after surgery. Plasma lactate and pyruvate concentrations, ketone bodies, C-peptide and counter-regulatory hormones were also measured. Glycaemia did not differ significantly in the two types of diabetes, regardless of the insulin therapy used. The amounts of insulin administered were similar in NIDDM and IDDM. There was no significant difference for other metabolic variables. Plasma concentrations of growth hormone (GH) increased significantly during surgery, especially in IDDM patients, but this change did not alter intraoperative glycaemic control. We conclude that mean glycaemic control, insulin requirements and development of ketone bodies in NIDDM and IDDM patients did not differ during the operative period, regardless of the insulin regimen used. Therefore, during the operative period, it is not necessary to modify the insulin regimen according to the type of diabetes. The consequences of increased plasma GH concentrations on glycaemic control in IDDM patients after operation are unknown.