To a remarkable extent, we owe our well-being, and in many cases our lives, to the work of one man and to events that happened 50 years ago this spring.

At 1 a.m. on March 21, 1963, an intense, irascible but modest Merck scientist named Maurice R. Hilleman was asleep at his home in the Philadelphia suburb of Lafayette Hill when his 5-year-old daughter, Jeryl Lynn, woke him with a sore throat. Dr. Hilleman felt the side of her face and then the telltale swelling beneath the jaw indicating mumps. He tucked her back into bed, about the only treatment anyone could offer at the time.

For most children, mumps was a nuisance disease, nothing worse than a painful swelling of the salivary glands. But Dr. Hilleman knew that it could sometimes leave a child deaf or otherwise permanently impaired.

He quickly dressed and drove 20 minutes to pick up proper sampling equipment from his laboratory. Returning home, he woke Jeryl Lynn long enough to swab the back of her throat and immerse the specimen in a nutrient broth. Then he drove back to store it in the laboratory freezer.

The name Maurice Hilleman may not ring a bell. But today 95 percent of American children receive the M.M.R. — the vaccine for measles, mumps and rubella that Dr. Hilleman invented, starting with the mumps strain he collected that night from his daughter.