&NA;A study of hemorrhagic shock in anemic dogs suggested a difference in pulmonary histopathology between animals treated with azathioprine and animals in a control group. Hemorrhagic shock for 2 hours without reinfusion produced definite changes in pulmonary anatomy by conventional histology and electron microscopy. The changes consisted of interstitial edema, vascular congestion, and focal atelectasis. Electron microscopic studies showed accumulation of edema fluid with disruption of Type II pneumocytes and the collagen fibrils in the alveolar‐capillary interstitium. Azathioprine ameliorated the shock state.