Aim. In vitro studies and animal experiments have provided evidence that albumin, bilirubin, meconium and inflammatory mediators act as surfactant inhibitors. The aim of this research was to establish whether their elevated concentrations in gastric aspirates, as representative samples of amniotic fluid, could contribute to the development of respiratory distress syndrome (RDS) in preterm infants. Methods. Infants born before the 35 th week of gestation between 1 March 1996 and 1 April 1997 were included. They were divided into two groups: the RDS and non RDS group. Gastric aspirates, taken immediately after birth, were used for biochemical measurements of albumin, bilirubin, meconium and E-α1-PI concentrations. Results. Sixty-one preterm infants were enrolled: 23 in the RDS group. The concentrations of albumin, bilirubin and meconium in gastric aspirates were higher in the RDS group (p < 0.01, p = 0.01 and p = 0.02, respectively). The E-α1-PI concentration showed no significant difference between the two groups. Logistic regression analysis showed that a markedly increased risk of RDS was only represented by albumin concentrations of over 1.6 mmol/l and gestational age of under 31 weeks. Conclusion. Our observations indicate that increased levels of albumin in the gastric aspirate, taken immediately after birth, may contribute to the development of RDS in preterm infants. Despite the established inhibitory effects of bilirubin, meconium and inflammatory mediators in vitro , we could not confirm their influence on the development of RDS.