Sydney Abbott had a toothache. She made an appointment with Dr. Randon Bragdon in Bangor, Maine, and routinely filled out his informational form. There she advised him that she carried the human immunodeficiency virus (HIV), precursor of AIDS. This was in September 1994.

The dentist located the problem in a lower molar but declined to risk filling the cavity in his office. He was agreeable to doing the work in the local hospital. She declined the offer, sued him and won her case under ADA - the Americans with Disabilities Act of 1990. On March 30, a puzzled Supreme Court heard argument in Bragdon's appeal.The Supremes had every right to be puzzled. From the time the ADA became effective in January 1992, the ambiguities of the act have puzzled lawyers and judges across the nation. The law deals chiefly with discrimination against the disabled in employment and public accommodation.

Through September 1997 (the latest available figure) 90,803 complaints of discrimination in employment alone had been filed with the Equal Employment Opportunity Commission. No one seems to know how many of the complaints of discrimination in public accommodations have materialized into lawsuits, but the number runs into the thousands.

In the case of the apprehensive dentist, the issue boiled down to the meaning of a few key words. The relevant portion of the act defines a "disability" in words that are covered with fuzz. A disability is a physical or mental impairment "that substantially limits one or more of the major life activities" of an individual. The act says that a place of public accommodation, such as a dentist's office, may not discriminate against a disabled person.

At oral argument, the Supremes chewed on the statute for an inconclusive hour. They found it hard to swallow. For one thing, Bragdon's patient was asymptomatic. She was living a full life. No impairment was visible. The justices wondered aloud if she were really "disabled" at all.

Does the mere presence of the virus substantially limit Abbott in a major life activity? Granted, reproduction is a major life activity, but the inert virus does not limit Abbott "substantially." Indeed, said counsel, she is free to copulate, conceive and give birth as she pleases. She is therefore not disabled, and she suffered no discrimination forbidden by the act.

It was hard to tell if the justices were impressed. Justice David Souter made the point that Abbott's decision to refrain from sexual intercourse, lest she pass the virus on to a partner or to a fetus, was a moral judgment, not a statutory requirement.

The ADA does not require an employer to hire anyone who might pose a "direct threat" to the health or safety of others. By extension, it seems plausible that if HIV constitutes a direct threat, dentists may be home free. If the virus is not a direct threat - an issue on which counsel disagreed - ADA will apply.

This was the first case under ADA to get to the Supreme Court. I'm sorry the court agreed to hear it. Other questions arising under this well-intentioned but obtuse act have far greater significance than the refusal of a dentist to fill a cavity.

In the seven years since ADA became operative, lower courts have struggled with complaints that Congress seems never to have foreseen. Many cases have to do with the problems in employment. Under the law, employers may not discriminate against a "qualified individual" with a disability. Such individuals are entitled to "reasonable accommodation" that will enable them to perform the essential functions of their employment.

You will see what a playpen Title I has created for lawyers. Qualified? Reasonable? Essential? Aggrieved employees have demanded - and courts have awarded - all kinds of privileges and benefits in the name of "reasonable accommodation." A leading case in 1993 involved a nonsmoker who won a smoke-free environment. But a would-be bus driver in Frederick County, Md., lost his claim. He had suffered two heart attacks in the four years preceding his application; he suffered from diabetes, and he had phlebitis in both legs. No accommodation would have been reasonable.

I wish the court had taken a case on "access." Owners of business property must provide access for disabled customers unless construction costs would impose an "undue burden." The law is far from clear on obesity as a disabling condition. The statute deals ambiguously with mental conditions, drug use and alcoholism.

We will learn a little bit about ADA from Bragdon vs. Abbott when an opinion comes down in June. A vast deal of interpretation will remain when the next century rolls around.