High resolution computed tomography (CT) was used to demonstrate the active lung phase of a patient with tocainide pulmonary toxicity. Gallium uptake in the lungs, an interstitial pneumonitis with alveolar macrophages on transbronchial biopsy, and reversal of process with discontinuation of the drug indicate a pulmonary drug reaction. The high resolution CT scan defined alveolar and interstitial components to the lung abnormality and correlated closely with the pathologic findings. High resolution CT is a useful method for demonstration of fine lung morphology.