This fall at Boston's Museum of Fine Arts thousands will view Claude Monet's last great works, among them his famous Water Lilies series. Thought by many to be the most beautiful landscape paintings in the world, they are the culmination of Monet's life's work, painted when he was in his 80s out of sheer love for the gardens he planted and cultivated for decades.

A few blocks down Huntington Avenue from the museum, Sid Rosen, 80, and Bob Krasner, 68, have enrolled at the School as M.P.H. students. Each in his own way is working, like Monet, toward the ultimate fulfillment of a lifelong passion. Rosen, an internist and gastroenterologist for 50 years in Fall River, Massachusetts, has come to the School to learn how to be a more effective advocate for doctors and patients in the increasingly contentious world of managed care. Krasner, from Rehoboth in southeastern Massachusetts, is topping off a 41-year teaching career at Providence College in Rhode Island--where he remains a tenured professor--with a textbook on microbiology. But before he sets pen to paper, he wants to avail himself of the global perspective the School has to offer.

Neither man has considered retiring, at least not in the conventional sense. "I've never been drawn to the kind of thinking that says you retire to Florida to play golf in the daytime and bridge in the evening," says Rosen, a former navy commander. "Why would I want to sit on the beach and bake my brains out when I can still be useful?" Krasner, who still plays the banjo in a group called the Red Suspenders Banjo Band, says, "I could retire, but I choose not to. I never played golf. The idea of moving to Florida and sitting around listening to a bunch of guys talking about their enlarged prostates doesn't much appeal to me."

Rosen says he set his sights on becoming a physician as a boy growing up in Lynn, Massachusetts, working at a soda fountain in a neighborhood pharmacy. "All the doctors came in there, so I met them all. It was very exciting for a kid. I knew even then what I wanted to do." He graduated from the University of Middlesex Medical School in 1943. Over the course of a career that began before the introduction of penicillin, Rosen says his love of medicine has never faltered. Rosen had begun treating the third generation of some of the families in his care in the working-class city of Fall River when, as he puts it: "The bureaucracy brought me to my knees. I needed a staff of five just to contend with the paperwork." But he views closing his practice as less a defeat than a tactical maneuver in the fight to preserve the values he has embraced all his life. "You can't mass produce health care like so many corrugated boxes," Rosen says. And so to better defend his beloved medicine, Rosen enrolled at Roger Williams University Law School in 1996 before deciding to shift course slightly, take a break from the law books, and earn his M.P.H.

Krasner says he began to appreciate the international dimensions of health and medicine during his service in the Army Medical Corps in Japan after World War II. A brief stint with the Public Health Service in Central America broadened his view of microbial disease and led him to consider the social, economic, and educational factors that influence the spread of infection. "That was my first glimpse of the big picture, and it's always been in the back of my mind to look again," he says. Krasner got his doctorate in biology from Boston University in 1956 and has been teaching at Providence College ever since. The microbiology text he is planning to write will be his legacy, and he wants to be sure it reflects the latest understanding of the global nature of illness, especially in light of emerging pathogens.

Both men credit their wives and grown children with encouraging them to pursue M.P.H. degrees, which is to say that each of them has experienced some hesitation from time to time. "When I first applied," Krasner recalls, "I worried that I wouldn't be an acceptable candidate because of my age. More recently I worried that I lacked the math skills I'd need, so I took a course in biostatistics to get ready. I'm working now to acquire the computer skills I need. But, hey, I know how to use a slide rule!" Rosen has also boned up on his math skills, taking courses during the last two summers. "I had to go back and learn how to use a scientific calculator. I had to relearn algebra which, by the way, I last encountered 60 years ago." Krasner admits that there have been days, especially during orientation and registration, when he found himself thinking, "Who am I kidding? I'm too old for this stuff!" But he's buoyed by his young colleagues. "One of my classmates, an M.D., is a Navy pilot who flies F-4s. He may be one of our astronauts one day. The school's so international--my classmates are the next generation of world leaders. It's terribly exciting! And I've always loved being around young people. Their enthusiasm for life is contagious."

Although Rosen's medical career spans more than four decades and reaches back to the days of house calls, he doesn't indulge much in nostalgia--the future is too exciting: "I was around when antibiotics were first developed, but I'll tell you that will be nothing compared to the great advances we're about to experience." Krasner remains in love with learning. "All my life, I've been cultivating my mind," he says. "I can't retire my mind. I can't just stop."

- Richard Hoffman