Sequence and structure are complementary properties of proteins that are critical for our understanding of the molecular machinery of living cells. VMD now makes the study of both easier than ever by integrating its structure viewing capabilities with a new sequence viewing window. Protein residues selected in the structure window can be highlighted in the new sequence window; conversely, the three-dimensional structure of segments selected from the new sequence window can be displayed in the structure window. With its powerful molecular graphics capabilities and its existing and planned sequence viewing tools, VMD has become an essential tool in biomedicine.