Five hundred seventeen agonistic encounters were observed between a total of 19 eastern chipmunks (Tamias striatus) in large outdoor cages. Encounters were classified as threats, chases, of fights, and the components of each are described in detail. The chipmunks exhibited a clear-cut, stable chase order which seemed more consistently correlated with size than with sex. The total number of encounters in which an animal was involved varied directly with rank. Mortality due to fighting occurred on 11 occasions. The individual killed was invariably low in the dominance order, even though the lower ranking animals were involved in fewer encounters than higher ranking ones. The dominance hierarchy apparently did not function to reduce the number or severity of encounters in the cage. Agonistic behavior observed in the field during the summers of 1964 and 1965 was qualitatively similar to that observed in the caged animals.