An extremely premature infant (24 weeks’ gestation, birth weight 380 g) with congenital heart disease and severe bronchopulmonary dysplasia is hospitalized for worsening respiratory function, hypoxia and rising eosinophilia in the absence of infection or cardiac decompensation. Poor weight gain is also noted. A Heiner syndrome - a rare non-IgE-mediated food hypersensitivity disorder affecting the lungs - is suspected. Elimination of cow’s milk and introduction of extensively hydrolysed formula result in clinical and laboratory improvement, further enhanced by a short course of systemic steroids. This case highlights the need to consider rare aetiologies such as Heiner syndrome in fragile neonates presenting with atypical respiratory symptoms and eosinophilia.