(CNN) -- Sen. Robert Byrd was hospitalized Monday night, a spokesman said.
Sen. Robert Byrd is expected to remain hospitalized overnight.
The 90-year-old Democrat from West Virginia appeared lethargic when he arrived at his Senate office Monday afternoon in preparation for a vote on global warming, the spokesman said.
After the vote, he returned home, where his caregiver noticed the same symptoms, took his temperature and discovered he had a fever, the spokesman said.
Upon the recommendation of his doctor, who was reached by telephone, Byrd was taken to a hospital, where he was expected to remain overnight for observation, the spokesman said.
Byrd, the Senate's longest-serving member and third in line to the presidency, was admitted in February to Washington's Walter Reed Army Medical Center for observation after a fall at his home.
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