Agonistic behavior between adult ♂♂ of the tropical cockroach Eublaberus posticus was studied. Observations were made under red light (590–640 nm) during the dark phase of a 12: 12 DL cycle, and recorded on a dictation instrument. Agonistic behavior appears to be causally related to territoriality. Social hierarchies are established and maintained by agonistic behavior. The application of information theory to the data shows that more information is transferred from the responder (eventual loser) to the initiator (eventual winner) of an agonistic encounter than from the initiator to the responder. A measure of information called normalized transmission is calculated which can be used to compare different species.