An increasing number of instructors are seeking to provide students with online anatomy resources. Many researchers have attempted to identify associations between resource use and student learning but few studies discuss the importance of usability testing in resource design and modification. Usability testing provides information about ease of use and resource flexibility and indicates navigational issues that contribute to extraneous cognitive load for the user. An example of usability testing for modification of an online anatomy resource called the "Virtual Lab" is presented. Usability testing was used to determine whether increased content would impair navigation through the interface. Subjects with varying levels of experience with anatomy content were recruited to assess efficiency and effectiveness (defined by usability standards) of the original resource and of the redesigned resource. Comparisons between usability evaluation of the original "Virtual Lab" (OVL) and of the redesigned "Virtual Lab" (RVL) revealed that subjects were better able to successfully complete tasks using the RVL than they were with the OVL. Results also demonstrated that subjects did not take significantly more time to successfully complete tasks with the RVL. Additionally, usability testing revealed that subjects were able to successfully complete tasks using the RVL regardless of whether they possessed prior experience with anatomy content or not. Results of this study suggest that the modified resource is more effective for users. The example presented here underscores the need for usability testing prior to resource implementation and whenever significant changes are made to a resource interface. (Contains 1 table and 4 figures.)