In the context of animal experimentation, laboratory workers fluctuate between seeing animals used in research as tools or objects and seeing them as sentient living beings. Most laboratory workers do not wholly lose their empathy and their ability to connect with other living beings. To deal with the fact that their job involves harming and killing animals on a regular basis, they employ various coping strategies, such as rationalizing the use of animals in research and minimizing their emotional attachment to (...) the animals. The evidence compiled in this article suggests that researchers, technicians, and caregivers who are involved in animal experimentation experience stress, anxiety, guilt, and trauma. I conclude that inflicting pain and death on nonhuman animals causes laboratory workers to suffer as well. Thus, in animal research, the suffering of nonhuman animals and humans is directly linked. The consideration of human suffering adds another dimension to ethical discussions of animal research, namely the relation between the suffering of human and nonhuman animals. A comprehensive ethical discussion of animal experiments should therefore include the suffering of nonhuman animals, the suffering of humans, and the relation between the two. (shrink)