An adult female olive baboon was paired with an adult male rhesus monkey in order to study interspecies social behavior. On
the eleventh day of the pairing the subjects began reciprocal vocal communication which occurred in the context of appeasement.
The sounds appear to contribute to a general reduction of tension between the two subjects.
This research was supported by U.S. Public Health Service research grants MH22253 toG. Mitchell, HD04335 toL. Chapman and RR00169 to the California Primate Research Center. The authors wish to acknowledge the technical assistance ofG. Burnside, Drs.R. Henrickson, R. Ringen, andJ. Erwin.