This paper examines how policy learning occurs in fields heavily reliant on regulatory science, such as environmental chemical risk assessment. It explores how institutionalized procedures can adapt to new scientific methods without alienating stakeholders who prefer stability. Through a survey of participants in an international ecotoxicology policy forum, the study finds that while open and balanced forums are beneficial, they may not always lead to efficient policy learning due to skepticism about scientific advances and their potential to introduce regulatory uncertainty. The longevity of participants in forums is also crucial for effective learning.