To investigate the mechanisms that sustains arterial hypertension in chronic uremia we performed hemodynamic studies in 13 dialysed uremics by means selective radiocardiography (Donato-Giuntini method). The 5 dialysed patients with dialysis controllable hypertension (GROUP B) had higher cardiac indexes (CI) respect to the 8 dialysed normotensive controls (GROUP A) (CI: Group B 4,250 l/min/m2, Group A 3,610 l/min/m2; p less than 0,05). The higher CI in group B appeared independent from the degree of anemia because the two groups had comparable hematocrit values (Hct:Group B 26,2% Group A 26,4%); On the other hand the slight blood volume expansion we observed in group B (7%) respect to group A hardly explains the observed difference in CI. It is interesting that pulmonary blood volume/total blood volume ratio (PBV/TBV) was significantly higher in dialysed hypertensives (PBV/TBV: Group B 14,26%, Group A 11,15%; p less than 0,05) The higher PBV/TBV can be the result of a decrease in venous compliance and could explain the higher CI in group B; further studies however are warranted to elucidate this point.