Isolation-reared rats exhibited enhanced behavioural responses to novelty, but only some aspects of such behavior was affected. In Experiment 1, environmental neophobia was enhanced but food neophobia was diminished in isolation-reared rats compared to socially reared rats. However, in Experiment 2, when subjects were not handled extensively prior to testing, no differences in behavioural responses to environmental or food novelty in an open-field were observed between rearing groups. The difference between these experiments was hypothesized to be the result of ceiling effects produced by increased anxiety or arousal in experiment 2 in which the animals had not been extensively handled. In summary, in these experiments anticipatory responses to novelty were alterred by isolation-rearing but the behavioural expression of this increased sensitivity was determined by intrinsic aversive/rewarding or arousing qualities of novel environments and novel foods.