Developmental factors are known to contribute to behavioural disorders related to fear and anxiety. Based upon the established association between restricted early life experiences and the development of inappropriate avoidance and fear-related aggressive behaviour, a series of experiments was designed to test whether a dog's capacity to remain in emotional homeostasis at 7 to 8 weeks of age can be increased by exposure to video images during the period of parasympathetic dominance between 3 and 5 weeks of age. First, it was demonstrated that puppies between 3 and 5 weeks of age do react to video images. Second, the reactions of puppies, exposed to video images for 30 minutes per day for 14 days between 3 and 5 weeks old, to test objects in both familiar and unfamiliar environments, were compared with those of control, unexposed puppies; the control puppies visited most of the objects significantly more frequently than did the exposed puppies. Third, another sample of puppies given the same treatments was tested at 7-8 weeks of age; the control puppies were significantly more fearful than the exposed, and also tended to visit the objects more frequently. A new classification of one class of problem behaviour related to anxiety and fear, separation problems. was developed and validated using a retrospective study of clinical data. In the same data. no evidence was found that a restricted maternal environment predisposed puppies to the development of separation problems; indeed, puppies raised in domestic maternal environments, seemed to be predisposed to have separation problems if they were homed at 7 weeks, but not at or after 8 weeks of age. Lxposure to busy urban environments on a regular basis post vaccination, seemed to protel:t against separation problems triggered by noxious events.