Pulmonary toxicity is an infrequent but serious adverse event in patients treated with amiodarone. The main problem at present is that we lack the necessary tools to detect this event or predict which patients will develop pulmonary toxicity. Serum Krebs von den Lungen-6 (KL-6) has been previously recognized as a marker for the activity of diffuse interstitial lung disease. We describe a patient with pulmonary toxicity due to amiodarone with increased blood levels of this new marker, and discuss the clinical usefulness of this new diagnostic tool.