This study examined preservice science teachers' understandings of the structure and function of the human gastrointestinal and endocrine systems through drawings and interviews. Moreover, the preservice science teachers described where they thought they learned about the systems. The 142 preservice teachers were asked to draw the human gastrointestinal and endocrine systems and label the organs. Following the in class drawings, the preservice science teachers were interviewed by a classmate about the drawing, the function of the system, and where they believed they learned about the system. The study provided evidence that (1) preservice science teachers had more knowledge of the gastrointestinal system than the endocrine system; (2) the interviews yielded more information about the systems than did the drawings; (3) food was described as moving from the mouth to the anus, but absorption was not often mentioned; and (4) the prior social interactions that influenced the knowledge of the preservice science teachers were different for the gastrointestinal and endocrine systems.