We compared dynamic lung compliance (Cldyn) determined by the oesophageal balloon technique with static compliance of the respiratory system (Crs) determined by an airway occlusion technique in 10 newborn infants with various cardio-respiratory diseases. The correlation between the two variables was linear and statistically significant (r = 0.911, p less than 0.0003; Cldyn = 1.51.Crs-0.48). Crs varied significantly less than Cldyn (mean coefficient of variation 3.9 for Crs vs. 9.3 for Cldyn; t = 6.06, p less than 0.0002). Since Crs is closely related to lung compliance but a more reliable parameter and technically easier to assess, we recommend the assessment of Crs instead of Cldyn in clinical practice.