One of China's most prominent human rights campaigners, Jiang Tianyong, has disappeared during a trip to visit relatives of a detained rights lawyer, Jiang's wife said.
Jiang, a legal activist, has not been heard from since Monday, when he was due to board a train to return to Beijing, his wife, Jin Bianling, said on Thursday.
Jiang's defence work involved some of China's most politically sensitive figures in recent years, including the dissident lawyer Gao Zhisheng and blind activist Chen Guangcheng.
Jiang was disbarred in 2009 but has continued his activism, recently helping to publicise the plight of nearly two dozen lawyers arrested as part of a sweeping 2015 government crackdown.
He could not be reached on Thursday on his mobile phone, which was turned off.
Jiang told the Associated Press news agency in June that he feared he could be arrested at any moment and rarely spent more than a few nights in one place.
Speaking by telephone from California, Jin said her husband's family sought to file a missing person report in his city of registered residence, Zhengzhou, in central China, but police turned them away and told to seek information in Beijing instead.
The Ministry of Public Security in Beijing did not immediately respond to a fax requesting comment about Jiang's whereabouts.