Duchenne muscolar dystrophy (DMD) is characterized by progressive skeletal muscle weakness. In small airways of wild -type (WT) mice, we previously showed increased bronchial epithelium thickness induced by low-intensity endurance training (Chimenti et al, AJRCCM 2007). No study has examined whether bronchiolar epithelium of dystrophin-deficient (MDX) mice shows any difference compared to WT mice and the effects of low-intensity endurance training. Bronchiolar epithelium thickness (Epithelial Area/Basement Membrane, EA/BM; BM length <1mm) was examined in formalin-fixed paraffin-embedded lung sections from male adult MDX (C57BL/10ScSn-Dmdmdx/J) and WT (C57Bl/10ScSn) mice after 6 weeks of treadmill training 5 days/wk at progressively increasing load (Exercise, EX), and 2 wks after cessation of training (Recovery, R). Sedentary controls (SD) at 0, 6 and 8 wks did not show any significant change in either WT or MDX mice, and pooled data were used for comparisons vs trained mice. MDX mice showed increased EA/BM compared to WT mice at all time points (MDX: 21.1± 3.8 mm, WT: 18.6±3.4 mm, p<0.0001). MDX mice also showed no training-induced changes in EA/BM. Conversely, in WT mice EA/BM increased after EX (WT-EX: 20.5±3.9 mm, WT-SD: 17.2±2.3 mm, p<0.0001) and decreased during R (WT-EX-R: 17.4±1.8 mm, p<0.005 vs WT-EX). These preliminary data suggest previously unknown structural abnormalities of the small airways in MDX mice. Data in WT mice extend our previously results by showing that EX-induced changes in small airways revert after interruption of training.