Vigor was the byword of the Kennedy years. After the wrinkled decorum of Dwight and Mamie Eisenhower, John F. Kennedy's America would feature people like him, the kind whose hair waved in the wind as they scrimmaged on the lawn at Hyannis Port, Mass. But for more than a decade now, as biographers have burrowed under the New Frontier, another J.F.K. has come into the picture. That would be the one with a multitude of serious illnesses whose life was a hidden ordeal of pills and injections, the one whose severe chronic back pain led him eventually to find relief in amphetamine shots from Max Jacobson, the celebrity physician later known as Dr. Feelgood. "I don't care if it's horse piss," Kennedy is reported to have told his disapproving brother Bobby. "It works."

Now enter Robert Dallek, a well-known historian of the presidency, bearing another stack of evidence and more bad news. At work on a Kennedy biography, Dallek became the first scholar to examine J.F.K.'s medical records on file at the Kennedy presidential library in Boston. Somewhat to Dallek's surprise, a summation of his discoveries published in the December issue of the Atlantic Monthly has set off a firestorm. It's not news that J.F.K. was in poor health much of the time, but Dallek paints the fullest and most unnerving picture yet of a President in constant pain from degenerative bone disease and heavily medicated. It raises the obvious question of whether voters should have known more about the health of a man who Dallek says often could barely climb a flight of stairs and could not put on his own socks. Dallek describes X rays showing that some of J.F.K.'s vertebrae collapsed while he was still in his 30s. The historian also learned that J.F.K. had nine secret hospital stays during a 2 1/2-year period in the mid-1950s.

"When I read about the hospitalizations, my eyes widened," says Dallek. "We never knew about this." Another revelation was the sheer quantity of medications Kennedy took daily during his presidency. "Steroids for his Addison's disease," Dallek writes, "pain-killers for his back, antispasmodics for his colitis, antibiotics for urinary-tract infections, antihistamines for allergies and, on at least one occasion, an antipsychotic (though only for two days) for a severe mood change that Jackie Kennedy believed had been brought on by the antihistamines." Johnny, we hardly knew ye.

Dallek believes that many of Kennedy's worst difficulties can be traced to the corticosteroids he took, perhaps starting as early as 1937, to relieve his colitis, an ulcerous inflammation of the upper bowel. Their heavy long-term use can promote osteoporosis  progressive bone disintegration. They also suppress the body's immune system, leading to the kind of serious infections Kennedy frequently suffered. But other common side effects are hair that stays thick and dark, plus skin that turns the yellow-gold of a permanent suntan. Another would be intensified sexual drive. All of which suggest that Kennedy's very Kennedy-ness was partly a side effect of his medication.

In 1947 J.F.K., then 30, learned he had Addison's disease, a dysfunction of the adrenal glands that, among other things, regulate blood sugar and the body's response to stress. The treatment? More corticosteroids. In the years that followed, as he rose from Congressman to Senator to presidential hopeful, Kennedy denied rumors of Addison's, some of them passed along to reporters by political opponents like Lyndon Johnson. He finally admitted to it in 1960, more or less, when he issued a statement acknowledging an "adrenal deficiency."

Kennedy's bad back was harder to deny, especially after near-fatal back surgery in 1954, when he was a Senator too much in the public eye to disappear for the eight months he needed to recover. But the back was absorbed into his legend, laid to football injuries and his indisputable heroism during World War II, explanations that merely buffed the chrome of J.F.K.'s image.

Historians have long complained that Kennedy's inner circle has been secretive and worse about his health. While preparing his 1993 book President Kennedy: Profile of Power, Richard Reeves requested access to J.F.K.'s medical records but was refused. He did succeed in interviewing the surgeons who performed the 1954 back operation, as well as Dr. Hans Kraus, who oversaw J.F.K.'s physical therapy in the last months of his presidency. "All of them told me they were asked to destroy certain records," says Reeves. "And they did."