Studies of the treatment of panic anxiety and various other states with monoamine oxidase (MAO) inhibitors are critically reviewed. It is concluded that MAOIs have differential effects on several dimensions of pathologic anxiety. The association between depression and anxiety states is also reviewed; it is observed that MAOIs effectively treat severe anxiety and phobic disorders without operating strictly via their antidepressant mechanism. In addition, it is proposed that biologic depression and biologic anxiety should be considered to have some independence from one another. Guidelines for the clinical delineation of anxiety disorders are provided, and the clinical and research implications of the proposal for revision of DSM-III anxiety and phobic disorders section, are outlined in detail. It is suggested that anxiety and phobic disorders be classified into endogenous (disease) and exogenous (nondisease) types.