The aim of this study was to evaluate the effects of living animals on pupils' intrinsic motivation and knowledge. Various studies from the late 1970s and 1980s stress the high effectiveness of authentic learning experiences in pupils' knowledge acquisition. However, there are only few current empirical studies on this topic. The research question of our study is to assess whether the use of living animals in the biology classroom supports intrinsic motivation and knowledge acquisition. In a pre-/post-test design, 185 fifth graders received two different treatments: the experimental group (N = 74) was taught with living harvest mice ("Micromys minutus") and the control group (N = 111) received lessons with the same content which was presented in short film clips on laptop computers. Knowledge acquisition was assessed with open-ended and closed questions, while intrinsic motivation was tested with an adapted version of the "Intrinsic Motivation Inventory" (IMI). There were no differences in knowledge acquisition between the treatments. However, the results of the IMI showed significant differences in favour of the experimental group in interest/enjoyment, perceived competence, and perceived autonomy. Thus, living animals exert a positive influence on motivation. (Contains 2 tables and 3 figures.)