The authors studied the motivation of nonhuman animal protectors engaged in caring for homeless animals. They were compared with individuals not involved in this activity. There were two hypotheses regarding the motivation. One hypothesis proposed animal protection is a substitute for people not satisfied with their family life and/or work. Another hypothesis suggested personality traits made some individuals attentive to the plight of humans and animals. The authors gathered demographic information and used an inventory on altruism toward humans and animals. (...) There were no distinctions in demographics. The factor analysis of the inventory revealed two factors. One factor was altruism toward animals and another factor was altruism toward humans. Animal protectors scored high on the first factor and low on the second. Non-animal protectors demonstrated the opposite distribution of scores. This is inconsistent with the second hypothesis. Altruism toward animals and altruism toward humans may result from different mechanisms. (shrink)