Iopydone is a pyridine derivative patented by Schering-Kahlbaum A.-G. As radiographic contrast medium for bronchography. Hytrast, an aqueous suspension containing Iopydol and Iopydone has widely used in some countries. Extensive clinical trials had suggested that Hytrast was superior to products usually employed for this purpose. Hytrast provides excellent quality bronchograms with a fine dense coating of the bronchial walls and no ‘alveolar filling’.