When the once-robust, telegenic man was wheeled in through the sliding glass doors of the plush Rudolfinerhaus hospital in early September, he was severely ill, conscious but groggy and complaining of terrible abdominal pain. Multiple blood tests were abnormal, doctors here say; his skin was covered with odd-looking lesions; his digestive tract was dotted with ulcers from top to bottom. Europe's most illustrious doctors were stumped; the patient's many symptoms defied a unifying diagnosis. Eight days later, Viktor A. Yushchenko, Ukraine's opposition leader, checked out against medical advice, determined to return to the business of winning the presidential election in...