We investigated exercise induced urinary albumin excretion rate (UAE)(ex-UAE) in patients with borderline hypertension (BH) compared to normotensives with positive-PFH and negative-NFH family history of hypertension. The study population consisted of 20 young, non-obese males with BH defined according to WHO criteria and confirmed by 24 h ambulatory blood pressure (ABP) and 40 healthy matched normotensives (PFH = 20 and NFH = 20). Twenty-four hour UAE was assessed by day and night time urine collection. BH and normotensive subjects performed a 20 min ergometric graded exercise test. The relationship between 24 h UAE, 24 h ABP and 2-D-echocardiographic left ventricular mass index (LVMI) were examined. The three groups did not differ in 24 h UAE. Exercise induced a significant increase in UAE only in BH. Exercise induced UAE was greater in BH compared to normotensives: BH = 54.3(21-125), PFH = 37.6(13-62), NFH = 9.7(0-35)micrograms/min, data expressed as median (I quartile-III quartile). Pooled data from all three groups showed a positive correlation between ex-UAE and systolic BP (SBP) during night time (by multiple regression analysis). In conclusion, BH without other known cardiovascular risk factors, moderate dynamic exercise induced an excessive increase in UAE.