Plasma glucose control and arterial pressure were assessed in 28 Type 1 (insulin-dependent) diabetic patients with different degrees of micro-albuminuria. They were divided into two groups according to their urinary albumin excretion rate: a low micro-albuminuria group (n = 16) with albumin excretion ranging between 12.1 and 28.9 micrograms/min and a high micro-albuminuria group (n = 12) with albumin excretion between 32.4 and 91.3 micrograms/min. The groups were matched for age, sex and duration of diabetes with the same number of normo-albuminuric (2.0-10.4 micrograms/min) diabetic control subjects. Both the low and high micro-albuminuria groups had significantly higher glycosylated haemoglobin levels and mean plasma glucose concentrations during a 24-h profile than their respective normo-albuminuric control subjects. A correlation between glycosylated haemoglobin level and urinary albumin excretion rate was found in the whole study group (r = 0.48; p less than 0.001). Arterial pressure (both systolic and diastolic) was significantly higher in the high micro-albuminuria group than in either the control group or the low micro-albuminuria group. A significant correlation was found between arterial pressure and albumin excretion rate in the whole study population (r = 0.49; p less than 0.001) as well as in the pooled micro-albuminuria groups (r = 0.43; p less than 0.05). Multiple regression analysis showed that glycosylated haemoglobin and arterial pressure levels were independently correlated with albumin excretion rates. Diabetic patients with micro-albuminuria of any degree have worse glycaemic control than normo-albuminuric patients.(ABSTRACT TRUNCATED AT 250 WORDS)