Ten insulin dependent diabetic patients were maintained in normoglycaemia for 36 h with an artificial pancreas. Circulating polymorphonuclear leucocytes were extracted and incubated with staphylococcus before and after treatment; phagocytic and bactericidal activities were studied. Granulocytes from diabetic patients showed a decreased ability to absorb staphylococcus and a reduced capacity for intracellular destruction of bacteria. These two functions were improved after 36 h of normoglycaemia but were not corrected.