Microalbuminuria was originally considered to be an important new risk factor 
for diabetic nephropathy. More recently, it has been convincingly shown that 
microalbuminuria is also an independent risk factor for cardiovascular morbidity 
and mortality in Type 1 and Type 2 diabetic patients. Even in the non-diabetic 
background population, microalbuminuria is a risk factor for cardiovascular 
mortality. What is the link between increased loss of albumin in urine and 
cardiovascular disease and mortality? As microalbuminuria is apparently 
associated with increased universal vascular sieving of albumin in terms of the 
transcapillary escape rate of albumin (TER-alb), microalbuminuria may reflect 
this universal sieving. The pathophysiology of increased TER-alb is unknown, but 
could be caused by haemodynamics or damage to the functional properties of the 
vascular wall. A number of studies have provided evidence of endothelial 
dysfunction in patients with microalbuminuria, which may be the common link 
accounting for the associations mentioned above. In this context, a number of 
markers of endothelial cell dysfunction have been found to be increased in 
patients with microalbuminuria. In addition, a number of functional in vivo 
tests of endothelial dysfunction have been performed in Type 1 and Type 2 
diabetic patients as well as in normal controls. Overall, these studies indicate 
the existence of a functional vascular dysfunction in Type 1 diabetic patients 
and normal controls with microalbuminuria, which may be related to dysfunction 
of endothelial cells.