The doctor asks his patient to say" Aahh" as he examines her throat. What comes out is a perfect note that fills the room. The patient is a professional singer, and the doctor a specialist, with an eye for details and an ear of music.

For opera singers, teachers and rock and roll musicians, a clear voice is not just a means of communication, it's their livelihood. So when their vocal cords are attacked by enemies ranging from the common cold to cancer, many don't waste a minute and go straight to Dr. Stephen M. Zeitels, assistant processor of otology and laryngology at the Medical School.

Zeitels specializes in treating a whole spectrum of problems related to the throat and vocal cords.

"I often see my patients perform," says Zeitels. "Usually I know what's playing [in town] because they come to see me the day before."

So why is Zeitels such a busy man?

"Boston has one of the largest concentrations of academic voices," he says. Zeitels cites Boston University, the New England Conservatory of Music and the Boston Symphony Orchestra as sources of many of his clients.

Zeitels has a formal arrangement to take care of visiting performers for the Boston Symphony Orchestra.

"We're relied on him and I know everyone thinks so highly of him," says Caroline E. Smedzig, spokesperson for the orchestra. "He's wonderful and we couldn't live without him."

Emily L. Raymer, assistant to the artistic administrator of the Boston Symphony Orchestra and a singer herself, says, 'We send everyone [who has problems] to him." Raymer cited world-renowned opera singer Frederica cited world-renowned opera singer Frederica von Stade as just one of Zeitels' famous patients.

Riding up the elevator, Zeitels bumps into a former patient. The man had cancer in his vocal cords, but it was detected early enough to be removed with a special procedure, allowing him to retain his original speaking voice.

Zeitels explains that diagnosing vocal problems can require both the perceptiveness of a singer's ear and the keenness of a surgeon's eye.

Often students are sent to him by their singing teachers. "They can hear a problem, while my ear is not good enough, yet [with proper instruments] I can see everything," says Zeitels.

The production of the human voice is a very complicated process, explains Zeitels, "The brain tells the vocal cords how tense to be and what shape to take."

The voice box, or larynx, then resonates inside the head to produce a tone. "Outside of the head it might sound like a trumpet mouthpiece with no trumpet," he explains.

Zeitels says he enjoys the challenge of working with such a delicate and finely-tuned organ of the body. "Life as a doctor is controlled chaos," says Zeitels, as he hustles from one examination room to the next, taking care of the waiting patients.

But seeing patients is just one facet of his work. Zeitels is also active in both teaching and research.

The Mass. Eye and Ear Infirmary is the seat of the Medical School's Otolaryngology Department. Aside from his primary appointment with Harvard, Zeitels also holds an adjunct appointment at the Boston University Medical School and is a lecturer at Tuffs Medical School.

In addition to training young physicians, Zeitels also teaches students of voice at Tanglewood, the Berklee College of Music.

"I teach them how they produce sound and how to take care of themselves--vocal hygiene," says Zeitels.

Zeitels' two main areas of specialization are cancer management and voice maintenance. He cites the variety in his patient population as being one of the most exciting parts of his job.

"[In this field], I deal with all age groups and types of people, from some of the sickest head and neck cancers to athletes of voice, performing artists," says Zeitels. "For example, I have a patient currently on the ward with a very serious cancer. This is very different from seeing the lead in a play."

When asked, he said that he often gets requests to make a house call in the dressing room of a performer, but he rarely does this, because of the lack of resources and equipment available in such a setting. "It would take the direst of circumstances," he says, to warrant such a visit.

Zeitels is also actively involved in improving techniques and instruments for working on and examining the throat. Some of his work has involved collaborating with an instrument company to patent tools for microlaryngeal surgery, which is performed with both lasers and conventional techniques.

Jerome Gropper, Zeitels' nursing assistant in the ear, nose and throat department, explains that the doctor's reputation has spread by word of mouth through the music community.

"They know him," says Gropper.