Amiodarone is a Class III antiarrhythmic agent that has been implicated as a cause of human pulmonary fibrosis. Pulmonary fibrosis is associated with increased levels of connective tissue proteins such as collagen and elastin. The purpose of this investigation was to determine whether elastin synthesis would be altered by in vitro amiodarone administration. Primary hamster lung cell cultures were utilized. Cultures were treated with 2, 10, and 20 micrograms/ml amiodarone. Following treatment, elastin synthesis was monitored by a biochemical tracer assay based on the presence of the cross-linking amino acids: desmosine/isodesmosine. These cross-links are found only in elastin. Addition of [14C] lysine to cultures results in uptake of the radiolabel into the cross-links. Cross-links were isolated and identified using chromatography and electrophoresis. At all doses of amiodarone, elastin synthesis was seen to increase above control levels. Light and electron microscopy confirmed the presence of an extracellular matrix. The morphologic studies also revealed the presence of cytoplasmic inclusion bodies and vacuoles that are often associated with cationic, amphiphilic drugs such as amiodarone.