Pulmonary reactions to drugs may be idiosyncratic or dose related and include diffuse alveolar damage, intra-alveolar hemorrhage, nonspecific interstitial pneumonia, usual interstitial pneumonia, organizing pneumonia, lymphocytic interstitial pneumonia, giant cell interstitial pneumonia, pulmonary edema, granulomatous interstitial pneumonia, pulmonary hypertension, and eosinophilic pneumonia. Transbronchial biopsy may be sufficient to diagnose many of these patterns, but because these patterns are nonspecific and may be caused by many other etiologies, a definitive diagnosis of drug reaction is not possible from the biopsy findings alone in most cases. Clinical history is of great importance in suggesting that the features on transbronchial biopsy are drug related. Table 28.1 lists the drugs that are well established as causes of pulmonary reactions. This list is not exhaustive, and it continues to grow as new drugs come to market or reactions to previously marketed drugs are documented.