In traditional medical histology courses, students have often used individual electron microscopic images to supplement their study of tissues at the light microscopic level. This new CD, Ultrastructure: An Interactive Virtual Electron Microscope, provides, in digital format, a more comprehensive view of cells and tissues at the ultrastructural level. Images (314 total, from 54 different specimens) were photographed on a Jeol 1200 EX-1 electron microscope; each slide includes one or more views at increasing magnification. Labels (revealed on rollover) amplify and explain fundamental aspects of the cell and tissue biology relevant to premedical science majors, medical students, and other students in allied health professions.