Abstract The effects of insulin-induced hypoglycaemia on the neutrophil respiratory burst were investigated in six patients with type 1 diabetes and six non-diabetic control subjects. Plasma glucose reached similar nadirs in control subjects (0.90.1 mmol l1; meanSEM) and diabetic patients (1.20.2 mmol l1) (NS). The resting neutrophil respiratory burst was similar in control subjects (1.260.15 mV) and diabetic patients (1.030.18 mV) (NS). The neutrophil respiratory burst fell following hypoglycaemia in control subjects and diabetic patients to 0.380.05 mV (P0.001) and 0.540.09 mV (P0.05), respectively. This fall was significantly greater in control subjects (ANOVA; P0.001). Resting neutrophil counts were not significantly different in control subjects (3.20.3109 l1) and diabetic patients (6.11.5109 l1). Following hypoglycaemia, neutrophil numbers increased in control subjects and diabetic patients to 11.51.4109 l1 (P0.01) and 9.71.7109 l1 (P0.05), respectively. This increase was significantly greater in control subjects (ANOVA; P0.001). These results suggest that the neutrophil respiratory burst is suppressed in response to hypoglycaemia and that this phenomenon is more pronounced in non-diabetic subjects.