From the Washington Post (link):
The Chinese government said Thursday that Vice Premier Huang Ju, one of the nine members of the Politburo Standing Committee, the nation’s secretive ruling council, had been hospitalized and was recovering. It did not specify the illness.
The statement by a government spokesman at a news conference was the first official comment on Huang’s unexplained absence since mid-January from all public events, including those attended by the other eight members of the committee.
Huang, 67, an influential former mayor of Shanghai who ranks sixth in the Communist Party hierarchy, is considered a close associate of former president Jiang Zemin. His disappearance has prompted discussion in party circles about whether allies of Jiang are being pushed aside by a rival faction led by his successor, Hu Jintao.
See also “What Is Up With Huang Ju?” from ESWN (scroll down the page).