We measured the partitioning of airflow between nasal and oral circuits in five species of lizards before, during and after exercise. Expired gases were measured separately from the mouth and nose circuits in order to estimate the relative contribution of each circuit to ventilatory airflow. Nasal breathing dominates before exercise; however, during exercise the breathing pattern switched to oronasal expiration. Airflow averaged 30% oral expiration across all species during and after exercise. These results have important implications for the design of appropriate masks for respirometry in lizards. In order to ensure that all gases are captured, it is critically important that both the nose and mouth circuits are sampled.