Anxiety observed in animals subjected to stress was stated in relation to anxiety level and biological backgrounds of animals, changes in neurotransmitters and causal stressors. 1. Anxiety is thought to be a negative emotion caused by many kinds of stress such as restraint stress, SART (specific alternation of rhythm in temperature) stress (a repeated cold stress caused by environmental temperature), social stress, etc. 2. Emotional behavior in those stressed animals were attenuated by anxiolytics like diazepam, a benzodiazepine receptor agonist and buspirone, a serotonin (5-HT) 1A agonist. 3. Stressed rats had changed brain levels of a variety of neurotransmitters such as corticotropin-releasing factor (CRF), noradrenaline, 5-HT, dopamine, acetylcholine, histamine, cholecystokinin, etc. The percentage of time spent on the open arms of an elevated plus-maze apparatus decreased in those stressed animals. Abnormal elevated plus-maze behaviors were attenuated by diazepam, buspiron and a CRF antagonist. 4. Anxiety level differs according to the coping strategy of the recipients. Rats of different strain, sex, aging and/or family display different behaviors in elevated plus-maze. 5. Stress-induced anxiety-related behaviors were observed when levels of some neurotransmitters became unbalanced. Thus modulators of unbalanced brain substances are thought to have anxiolytic properties.