Faculty and staff at the University of Arizona have developed an "interactive online resource for learning biology" based on an entry-level biology course, for use by high school and college-level students. The site is divided into seven subject areas: biochemistry, cell biology, developmental biology, human biology, Mendelian genetics, immunology, and molecular biology. Within each subject there are problem sets, tutorials, activities, and links to related Internet resources. This well-designed site can be used in combination with classroom or laboratory course work, or as a self-guided study program. The Biology Project is funded by a grant from the William and Flora Hewlett Foundation. The Guided Tour requires JavaScript.