Dr. Nancy E. Good's most demanding patient is the TV show "St. Elsewhere."

A former Navy internist now starting a practice in Long Beach, Calif., Good, 33, became the program's on-call physician last spring.

Her work begins once a basic plot line or rough script is assigned to the story editors to be turned into a finished script. "They call me about the medical things they want to do," she said, " and diseases or conditions are found to fit the story line or character."

A typical question Good might be asked is this one from story editor Channing Gibson: "If a certain character were going to have an existential crisis, what would be the medical case that would come in and do this to him?" In one episode, Good helped writers settle on the death of a homeless man in the emergency room as an event that triggers Dr. Wayne Fiscus' outburst over his frustration with city-hospital medicine.

Another recent episode called for surgeon Mark Craig to perform emergency surgery during a power blackout at the hospital. "Coming up with the condition that led to the emergency surgery . . . was my job," Good said. She suggested a gastrointestinal hemorrhage.

Most ideas originate with the writers, although they occasionally use Good's suggestions for scripts. "I'm surprised at how much medicine they know," said Good. She talks with the writers by telephone "several times a day" to answer questions and help with medical details on each script.

A native of Glendale, Calif., Good graduated from Yale Medical School and worked in naval hospitals in Japan, San Diego and Long Beach after completing her residency in internal medicine at Los Angeles County-USC Medical Center.

She is a longtime fan of "St. Elsewhere" and applied for the job of medical adviser when she heard last year that the position was open. She enjoys her work on the show, she said, because "I can be academic, and nobody's too sick."