A basic understanding of acid-base physiology is critical for the correct assessment of arterial blood gases in the clinical setting. In this context, collaborative teaching strategies in the undergraduate classroom setting may be useful, since it has been reported to enhance both transfer and retention of learned material in a time-efficient fashion. In a previous study, the authors found that conventional group work and peer instruction equally enabled second-year medical students to diagnose common acid-base disorders immediately after class, indicating successful transfer of the learned material. This article describes a 2-yr followup study in which they investigated whether these collaborative strategies also lead to long-term retention of the learned skills.