The DSM-III introduced Panic Disorder as a new diagnostic concept among the anxiety disorders. The justification for this was derived from data from biological psychiatry, especially the work of Donald Klein. In this article his model is critically reviewed. The following topics are discussed:

a. the presumed specific activity of antidepressives in panic disorder,

b. the possible relation between panic, separation anxiety and agoraphobia,

c. the search for a biological `marker' for PD,

d. genetic factors and PD.

In addition, two psychological models for the genetics of panic attacks are discussed. It is concluded that Klein's biological model has greatly stimulated research, but recent empirical data offer insufficient support for this specific model, although biological mechanisms seem important. In the conceptualization of panic anxiety more attention for psychological mechanisms is advocated.