Research in education suggests that computer games can serve as powerful learning environments, however, teachers perceive many obstacles to using games as teaching tools. In this study, we examine three science teachers' implementation and perceptions of a curriculum unit incorporating the game, Mission Biotech (MBt) and a set of supporting curriculum materials. The curriculum unit was designed to provide multiple avenues for teachers to adjust and modify materials and implementation plans based on their unique classroom goals and environments. To understand how individual teachers use, conceptualize, and reflect upon the MBt unit and its implementation, we conducted three case studies, including classroom observations and teacher interviews. Findings include many similarities among teachers including adaptation of activities to classroom norms and practices, high value placed on quality curricular resources and support, advantage of the game to provide experiences that are normally out of reach for students, and concerns about effective use of time. Unique features of different teachers revealed implications for design and professional development for game-based curricula. For example, the study revealed that teachers need support to integrate and make explicit connections between the game and supporting curriculum materials. (Contains 1 table and 2 figures.)