Rhesus monkeys sometimes develop self-injurious behavior that may include occasional wounding (SIB) with frequent bouts of non-injurious, self-directed biting (NIB) Only a small percentage of individually housed monkeys acquire this condition suggesting that individual, genetically-based, characteristics may increase susceptibility in some monkeys Certain temperamental characteristics such as high reactivity and impulsivity are known to be genetically-based The purpose of this study was to determine if a high reactive temperament, characteristic of 20% of the rhesus monkey population, was associated with this disorder High reactors show heightened and prolonged physiological reactions to novel events and typically have high, stable heart rate patterms Heart rate and interbeat variability were examined in monkeys with a veterinary record of SIB (n=11) and in control monkeys (n=9) Monkeys were fitted with vests containing radiotelemetry units in the earl y afternoo n and had their heart rate monitored remotely for a 30-minute period the next morning After 18 minutes of baseline, the monkeys were exposed to novel sound (buzzer) three times at 3-minute intervals and then briefly observed a human carrying a net Heart rate decreased significantly during the first 18 minutes There was little reaction to the buzzer, but heart rate increased rapidly in response to the human carrying a net Neither heart rate nor interbeat variability differed in SIB and control monkeys However, heart rate did vary as a function of the occurrence of non-injurious biting Seven of 11 SIB monkeys engaged in non-injurious biting (NIB) during heart rate testing and had significantly higher heart rates than the 4 non-biting monkeys Two control monkeys also showed unusual reactions to the heart rate testing by exhibiting high levels of non-injurious biting These two subjects had significantly higher heart rates than all other monkeys In most primates, heart rat e is negatively correlated with interbeat variability This relationship was observed in nonbiting controls but not in the monkeys that directed non-injurious bites to themselves during the procedure These data fail to provide a link between SIB or NIB and high reactive temperament However, the data clearly show a dysregulation of heart function in self-biting monkeys with the uncoupling of heart rate and interbeat variability Further research will be aimed at determining whether self-directed biting produces dysregulation in heart rate activity