Virtual slides are digital facsimiles of glass microscope slides that, when viewed with a pan and zoom viewer, can emulate viewing a glass slide with a traditional microscope. Based on successful implementation of virtual slides in medical student histology and pathology courses at the University of Iowa, we developed a plan to evaluate the use of virtual slides in the American Association for Cancer Research's annual Pathobiology of Cancer Workshop. In this Workshop, nonphysician predoctoral students and postdoctoral fellows working in cancer research explore the morphological, clinical, and molecular aspects of human cancer. Over the course of a week, students examine approximately 100 glass slides in microscope laboratories, facilitated by senior cancer investigators. The goal of the present study was to evaluate virtual slides as a teaching modality in these laboratories, not as a replacement for traditional microscopy, but rather in terms of their utility in facilitating student learning as they examine glass slides with a traditional microscope. Evaluation by questionnaire indicated that virtual slides enhanced students' ability to grasp morphological features better than the traditional photomicrographs. The results of this implementation suggest that virtual slide technology may be successfully extended to other educational venues where traditional microscopy and photomicrographs are currently used.