Environmental challenges during early life have been shown to result in greater risk of chronic diseases such as diabetes and coronary disease in later life. Factors such as unbalanced nutrition before birth result in metabolic and structural adaptations that lead to persistent modifications to offspring phenotype. There is evidence that respiratory disease is influenced by developmental environment.(1) Reduced fetal growth is associated with impaired lung development, and increased risk of COPD in later life. Our aim was to investigate whether exposure to a low protein diet in utero affects adult offspring lung morphology. Methods: Pregnant Wistar rats fed control (C, 18% casein) or protein restricted (PR, 9% casein) diet from conception to term (22days). Lung tissue was harvested (225 days F1) from male offspring. Left lung volumes were calculated from formalin perfused weights by volume displacement. Lungs were fixed for 24 hours in formalin then processed and embedded in paraffin wax before entire lung was sectioned. Sections were H and E stained, imaged at 10x magnification and point counted to give volume fractionation of selected areas. Other morphological measurements were made to estimate surface area; 10x magnification, and alveolar wall thickness; 63x magnification. There was no significant difference in lung weight and perfused lung volume or between amount of alveolar airspace, airways, airway components (lumen, epithelium and smooth muscle) vessel or vessel lumen between the two groups, PR and C in the 225 days F1. However there was a significant increase (p=0.046, T-test) in the amount of smooth muscle around the vessels in the protein restricted group compared to the control group for this time point. In this study there is no evidence to suggest that in utero exposure to maternal low protein diet has significantly affected adult lung physiology in 225 day old rats. The increased smooth muscle data however does suggest remodelling in the pulmonary arteries and may be indicative of pulmonary hypertension in this model.