Molecules is an application for viewing three-dimensional renderings of molecules and manipulating them using your fingers on iPhone, iPod touch, and iPad. You can rotate the molecules by moving your finger across the display, zoom in or out by using two-finger pinch gestures, or pan the molecule by moving two fingers across the screen at once. The application pushes the limits of mobile graphics processors by using advanced techniques to make realistic 3-D renderings of molecular models. New molecules can be downloaded from either the RCSB Protein Data Bank (http://www.rcsb.org/pdb), an international repository of biological molecules and their 3-D structures, or NCBI's PubChem (http://pubchem.ncbi.nlm.nih.gov). The application uses the Entrez Programming Utilities to perform a keyword search of PubChem's compound database, as well as to download 3-D structure definition files from that database. Molecules is a BSD-licensed open source project, with the latest source code available at the application's main page: http://www.sunsetlakesoftware.com/molecules .