Under Wisconsin law, as an example, the terms "mental disease or defect" do not include an abnormality manifested only by repeated criminal or otherwise antisocial conduct; mental disease or defect excludes responsibility for criminal acts. The mental disease or defect plea can be used in Wisconsin in a variety of ways: (1) raised as part of an argument that a defendant is not competent to stand trial; (2) used to exclude responsibility for a crime; (3) employed to reduce murder to manslaughter or another lesser offense; and (4) used to justify psychiatric testimony as relevant evidence of a defendant's mental state. A diagnosis of borderline personality disorder, when a psychosis is present, lends itself to elements of the insanity definition and is temporary in that the catastrophic event of murder requires the presence of the battering mate. It is arguable that the premenstrual syndrome diagnosis can be used as part of an insanity plea in cases of battered women who kill. One of the major concerns here is taking a physical problem experienced by many women and incorporating it in an insanity defense, thereby raising the notion that women are "insane" during certain times of the month. It is concluded that, despite some opposition, a defense attorney must investigate whether the battered woman who kills the abuser suffered from a mental disease or defect at the time of the crime. Characteristics of borderline personality, post-traumatic stress, and disassociative disorders are listed, along with proposed diagnostic categories requiring further study.