ABSTRACT.We studied urine excretion of free and conjugated aldosterone by 12 control infants and 14 infants with hyaline membrane disease (HMD) on the first and seventh days after birth. Both groups had a mean gestational age of 29 weeks. Total urine aldosterone excretion (UAE) and percent excreted as conjugate were similar for both groups on both study days, and did not relate to the severity of respiratory failure in infants with HMD. Sodium intake was higher for infants with HMD on both study days (p<0.02), but their urine sodium excretion was only significantly (p3 nmol/kg/d, there was no significant difference between estimated sodium‐potassium exchange by control (22 ± 5 %,n=8) and HMD (31 ± 5 %,n=10) groups. These data suggest that neither the magnitude of excretion of aldosterone in the urine, the ability to conjugate aldosterone nor the degree of relative distal tubular unresponsiveness to aldosterone are related to the severity of pulmonary immaturity in preterm infa