Behavioral disorders in companion animals, especially dogs, are a great concern. Due to the re- lationship between oxidative stress and behavior problems and also heavy metals’ capability of creating oxidative stress, in the current study, the effects of lead, mercury, arsenic, and cadmium on 13 common canine behavior problems (fearfulness, excessive barking, destructiveness, house soiling, inappropriate sexual behavior, coprophagia, wandering, shyness, aggression toward the owner, aggression toward familiar people, aggression toward strangers, aggression toward other dogs, and excessive activity) were evaluated. According to owners’ answers to the questionnaire, 43 terrier dogs were chosen. Of these 7 dogs showed no behavior problem and 36 dogs displayed at least one behavior problem. The blood concentrations of lead, mercury, arsenic, and cadmium were measured using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). No significant differences in heavy metal concentrations were observed between the case and control groups. However, the cadmium concentration was significantly elevated in dogs displayed aggres- sive behavior toward their owners (p < 0.048, n=5). while arsenic level was significantly lower in dogs displaying fearfulness (p = 0.048, n= 25). Results of the study reported here do not support the hypothesis that “blood concentration of heavy metals may influence the occurrence or pre- vention of common behavioral problems in dogs”. Our results suggest that there may be a direct relationship between higher levels of cadmium and aggression toward the owner and arsenic with reduced fearfulness in dogs. However, we have to consider that the behavioral effects of heavy metals are likely very complex

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