A comparative analysis was made of the public's attitudes toward the use of animals in scientific research in 15 different nations. The intensity of opposition to animal research was found to vary from relatively low levels in Japan and the United States to much higher levels in France, Belgium, and Great Britain. More women than men were opposed to animal research in all 15 nations. Scientific knowledge, or the lack of knowledge, was not found to have a consistent relationship with attitudes toward animal research. Concern about the environment was found to be related to opposition to animal research in some western European nations, in particular West Germany. Cluster analysis was used to group the nations into four patterns based on intensity of opposition, level of opposition, gender differences in opposition, and the relationship between attitudes toward animal research and both environmental concern and scientific knowledge.