ON DECEMBER 16, 1981, a Brooklyn woman named Shirley Santos--an unwed mother with six children--brought her four-year-old daughter to the hospital. Covered with welts and urinating blood, the child had clearly been the victim of a violent outburst. After only a few hours at the hospital, police arrested Santos on charges of child abuse. "I don't remember what happened," she told them. "I would never hurt my baby...I just got my period."

Although this excuse would have made little headway with judges a few years ago, the example of two English cases in which sentences were reduced because of the defendants' menstrual stress inspired Santos's lawyer to use it as a legal defense. Referring to her client's complaint by its medical moniker, Pre-Menstrual Syndrome (PMS), defense attorney Stephanie Benson claimed that Santos was suffering from an extreme case of PMS when she beat her child. Santos had blacked out because of the condition, Benson asserted; she was therefore unable to feel the "criminal intent" that would make her responsible for her actions.

Earlier this week, Benson dropped this controversial defense, in exchange for a guilty plea on the lesser charge of harassment. "I have long argued that there is no basis for the use of this defense," crowed Brooklyn District Attorney Elizabeth Holtzman, the prosecutor in the case. "The withdrawal of this defense is a signal that PMS is a defense without merit."

Holtzman is absolutely right. In the first place, little is known about the medical ramifications of PMS. Headaches, depression, swollen arms and legs, severe abdominal pain and violent outbursts have all been cited as symptoms of the syndrome, which, manifesting a wide range of quirks in a wide range of women, apparently follows no consistent pattern or course. Therefore, the court would have had to accept on faith Santos's claims that her menstrual stress related to her behavior.

In addition, while most American women experience some degree of menstrual or pre-menstrual discomfort, only a small number of these have ever reported the kind of rage that would cause an otherwise gentle mother to attack her child. Some question exists, therefore, about whether PMS can be properly classified as a disease at all; other aspects of a woman's physical or emotional health may have a significant impact on how she reacts under menstrual stress.

Even women who are pleased that the medical establishment has begun to look seriously at what has for too long been regarded as an insignificant problem in women's health warn against carrying things too far. "I have a lot of empathy for a woman who loses control under premenstrual stress," a member of a group called PMS Action told Newsweek last week. "Yet so little is known about PMS that use of it as a defense is premature."

But probably the most cogent argument against the use of PMS as a legal defense lies in its inherently anti-feminist stance. Those members of society who still believe that a woman can never be president of the United States because of her physiology will find in the PMS defense ample support for their views. In light of the scanty evidence, then, we must vigorously resist blaming a woman's irrational behavior on her biology. Until much more data on PMS is available, we must continue to trace acts of violence like Santos's to aberrant emotions, rather than to built-in biological flaws.