This report describes autonomic and behavioral measures that reliably discriminate two strains of pointer dogs. These two strains, one abnormal and the other normal in behavior, have been produced by a combination of inbreeding and selection. In this context, abnormal behavior means marked timidity, excessive startle, and catatonic-like immobility. The prepotent stimulus eliciting such “phobic” behavior is man.Discriminant analyses were done on 20 pathological and 19 normal dogs using behavioral measures alone, autonomic measures alone, and combined behavioral and autonomic measures. Resting heart rate (HR) as well as HR and electrocardiographic changes due to an intravenously administered parasympathetic blocker (atropine) and a sympathetic stimulant (isoproterenol) were studied. The combined battery of behavioral and autonomic variables separated the two strains of pointers with 100 per cent accuracy; behavioral measures alone and autonomic measures alone were 95 per cent accurate.To test the validity of the discriminant coefficients derived from the autonomic analysis, 10 additional animals were studied. The previously computed discriminant coefficients were blindly applied to this new sample. Of the 10 dogs, 9 were correctly identified as abnormal or normal (one misclassification). It would appear that in these animals, abnormal behavior has specific autonomic correlates.The results of this study along with hematological and CNS biochemical data from our laboratory are discussed in terms of brain mechanisms that might underlie the behavior of the pathological strain.