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.