The book demanded reform in Egypt and praised Mr ElBaradei
The Egyptian publisher of a book supporting the former UN nuclear watchdog head Mohamed ElBaradei has been released from jail, officials say.
Publisher Ahmed Mahanna was detained on Saturday and released a day later.
Mr ElBaradei, the former head of the International Atomic Energy Agency, has recently returned to Egypt and launched a campaign for political reform.
He is emerging as a potential challenger to Hosni Mubarak, who has been in power for nearly three decades.
The unnamed official did not give any reason for the detention, it was reported.
The Arab Network for Human Rights said that Ahmed Mahanna's office was raided and his computer confiscated.
Mr ElBaradei has hinted he may stand against 81-year-old President Mubarak, who has ruled since 1981, in an election due in 2011. Observers believe Mr Mubarak wants his son Gamal to succeed him.
Analysts say Mr ElBaradei's appeal for many Egyptians is that he is a civilian in a country long ruled by soldiers, and that he is untainted by corruption allegations.
But detractors writing in state media have portrayed him as a figure who is out of touch with Egyptian life, having lived abroad for so many years.
Mr ElBaradei, 67, built a strong reputation as head of the International Atomic Energy Agency (IAEA) and won the Nobel Peace Prize in 2005.