Start with the basic scenario. You are sitting in the doctor's office, dressed in one of those charming johnnies that open ever so attractively at the back.

The doctor has probed various parts of your body and history that are not generally open to public scrutiny. The doctor now knows your age and weight (well, more or less), your blood pressure, your medications, your symptoms past and present, your reproductive history and any drugs that have been prescribed.For that matter he or she may know what genetic tests you've had and what your HIV status is, whether you've taken Prozac and if that's your original nose.

You have agreed to this, stripped yourself of reticence along with your suit jacket and answered the questions as part of an implicit exchange. Patient tells all; doctor cures all.

But there is another assumption behind this deal: privacy. The doctor won't tell all. The doctor won't repeat your medical condition to your boss or storekeeper any more than he or she would publish snapshots of you having a mammogram.

This is what Dr. Denise Nagel of the National Coalition for Patient Rights calls "Medical Ethics 101." Indeed, the Hippocratic oath says, "That whatsoever I shall see or hear of the lives of men, which is not fitting to be spoken . . . I shall keep inviolably secret."

But like so many things in health care, that basic trust is suddenly on shaky ground. As Nagel says, "They have taken a safe harbor and turned it into a fish-bowl."

Over the past half-dozen years, changes in medical care and technological advances have put the intimate details of your life into some databank. The number of people in and out of medicine who may have access to that information has grown so wide that it gives new meaning to the word "private."

For many people, the first alarm about this lack of privacy came this summer with the belated realization that the 1996 medical portability act came with a hitch. The Department of Health and Human Ser-vices was instructed to come up with a national system that would give each of us a number, a unique health identifier, for every bit of medical information from womb to tomb.

The number would be an efficient way to pull up an entire medical history at 3 a.m. at the scene of an accident. A way to help track diseases and diseased people with the hope of improving treatment.

But anyone with access to the number could know your genetic predisposition for Alzheimer's and the time you took emergency contraception.

In the world of HMOs hired by employers, do you want a current or future boss to know your genetic predisposition to breast cancer? What effect would this have on your willingness to tell your doctor about depression or alcohol abuse?

When the debate over managed care resumes, any true patient's bill of rights has to include an enhanced right to privacy. We need the right to limit the information insurers can demand and allow people to opt out of tell-all consent forms. We also need some pretty stringent penalties for people who sell our medical history for marketing without permission.

The free exchange between patient and doctor is still at the heart of health care. Mistrust is bad for your health. And privacy is prescribed.