The web has the potential to offer an environment that can support standardized medical education to students dispersed in time or place and, in the process, respond to reduced availability of patients for practice. This exploratory article describes how we evaluated critical thinking in an online collaborative Problem-based Learning (PBL) tutorial built on a platform integrating a well-known course management system and a voice-over the Internet communications tool. We discuss the process and results of evaluating the tutorials by adapting and applying an earlier framework used to measure the level of critical thinking taking place in collaborative online PBL tutorials. Our results indicate that this framework could be used as a method to compare levels of critical thinking between tutorial groups as well as tutorial variables such as case study formats and the types of technology used to support the sessions. (Contains 5 tables.)