This study examined 148 adolescents' use of self-regulated learning (SRL) processes when learning about the circulatory system using hypermedia. We examined participants' verbal protocols to determine the relationship between SRL processes and qualitative shifts in students' mental models from pretest to posttest. Results indicated that participants who exhibited a qualitative shift displayed differential use of six SRL processes, including metacognitive monitoring activities, learning strategies, and indications of task difficulty. The authors propose that these SRL processes can account for the participants' shift in mental model. Implications for the design of hypermedia learning environments are presented, including substantive recommendations for the use of trace logs and scaffolding to promote self-regulated learning with hypermedia. Classes, Descriptions, and Examples of the Variables Used to Code Students' Regulatory Behavior (from Azevedo & Cromley, 2004)is appended. (Contains 2 tables.) [An earlier version of this article was presented at the 12th International Conference on Artificial Intelligence in Education, 2005 (Amsterdam, The Netherlands).]