As part of an investigation on the behavioral characteristics of SART-stressed animals, an animal model of autonomic imbalance, the open-field behavior of SART-stressed (repeated cold-stressed) rats was studied and compared with that of rats exposed to other types of stress. In addition, the effects of several drugs on it were also studied. As compared with normal rats, SART-stressed rats exhibited increased locomotor activity, rearing and center-field penetration, together with decreased grooming and increased defecation, whereas they showed no significant changes in spontaneous movements in the daytime as measured by an Animex activity meter. These behavioral abnormalities were remarkably different from those due to 1-hr cold, 48-hr cold and repeated restraint stresses. These abnormal forms of open-field behavior due to SART stress were considerably inhibited by chlorpromazine, imipramine and neurotropin at doses having no corresponding influence on normal rats; and they were partially inhibited by alprazolam, diazepam and carpipramine at doses exerting considerable influence on normal rats. The above results show that SART-stressed rats exhibit open-field behavioral abnormalities that are different from those of rats exposed to other types of stress. Such abnormalities include excessive activity, which is considered to be caused by excessive emotionality.