Orient have signed the Blues defender Sam Oji on a month long loan and he goes straight in the squad for tonight's Carling Cup match against Cardiff.
Twenty one year old Oji has made just one senior appearance for Birmingham but has played nine league games whilst on previous loans to Doncaster and Bristol Rovers.
Oji told the club's official website, "If I do well maybe I can stay here a little longer."
Oji, who will provide cover for the injured Brian Saah and Clayton Fortune, will wear the number 15 shirt.