Newborns are exposed to elevated oxidative stress during birth. Part of the adaptation mechanism is the degradation of foetal hemoglobin. Heme oxygenases are responsible for the catabolism of free hem. Heme oxygenase- 1 (HO-1) is the inducible isoform whitch is induced by hem and oxidative stress. We have previously demonstrated that HO-1 is induced in healthy mature newborns and premature infants with transient adaptation difficulty. In our present study we examined HO-1 gene expression in premature infants with serious disease based on oxidative stress. The HO-1 mRNA expression was measured from 100 μl venous blood sample by a competitive RT-PCR technique on the first, 3rd and 5th day after birth in 18 premature infants with respiratory distress syndrome (RDS). We found that HO-1 gene expression is significantly increased in prematures with RDS compared to the previously examined groups. Thus it seems HO-1 plays role not only during physiological adaptation but in the protection against oxidative cell injury in RDS.