The present study has been designed to examine the role of a hyperglycaemic spike of short duration as a factor possibly involved in haemorheological microcirculatory and (or) haemostatic dysfunctions in ten insulin-dependent diabetes mellitus patients (IDDM) and five healthy volunteers. The hyperglycaemic spike was induced by glucose infusion via GCIIS Biostator. Blood viscosity, erythrocyte aggregation, erythrocyte deformability, plasma viscosity and proteins' levels, cell counts, and transcutaneous oxygen pressure were investigated during normoglycaemic period and at the end of a 1 h hyperglycaemic spike. Hyperglycaemia induced in IDDM patients significant decreases in erythrocyte aggregation, in blood and plasma viscosities and in both fibrinogen and albumin levels. The number of platelets was significantly decreased as a result of the hyperglycaemic spike. There was no significant change induced by the hyperglycaemic spike in healthy volunteers. These findings show that a hyperglycaemic spike of 280 mg/dl (15.6 mmol/l) of short duration in IDDM patients causes numerous significant changes in both blood components and rheological behaviour. These changes were accompanied by a significant decrease in transcutaneous oxygen tension indicating an impaired tissue oxygenation during the hyperglycaemia.