Nicholas Clapton, the show's curator, said that about 70% of opera singers in the Italian baroque period from 1600 to 1750 were castrati because the Roman Catholic church forbade women to appear on stage.
They were male sopranos, mezzo-sopranos or contraltos.
Sarah Bardwell, director of the Handel House Museum in London where the exhibition is being held, said: "The castrati were the 18th century's superstars. They were celebrities, surrounded by money, fame."
Titled Handel and the Castrati, the show displays some of the surgical instruments, or castratori, used to obtain these tender, agile and magnificent voices that were the most applauded in their time.
"Castration was performed by cutting the blood supply to the testicles, or by amputating them altogether," Clapton said.
Castratori were used to cut blood
supply to or amputate testicles
The show includes paintings and prints of castrati.
However, it is above all a tribute to the voices and stories behind the castrated singers for whom Georg Friederich Handel (1685-1759) composed works.
It presents the original scores of pieces performed by Senesino, Nicolini, Bernacchi, Carestini, Caffarelli, Conti and Guadagni.
A relative of Francesco Bernardi Senesino, who lived from 1685 to 1759, travelled from Italy to London to see the tribute.
Clapton, a counter-tenor, said most of the singers were castrated at eight years old and they then devoted their lives to art, with "very intensive training" of six to eight hours a day.
"The finest of the boy sopranos were picked by music masters for castration," he said.
"As many as 4,000 boys were castrated annually in the service of art ... and, as pope Clement VIII said, 'to the honour of God'. They were neither man nor woman, but something in between. They were stars ... but also taunted"
"As many as 4,000 boys were castrated annually in the service of art ... and, as pope Clement VIII said, 'to the honour of God'.
"The castrati would have the high voice of a boy soprano, but the lung power of a full-grown man.
"They had amazingly powerful and high voices. They were neither man nor woman, but something in between. They were stars, they were admired, had adoring fans ... but also taunted."
The last of the castrati was Alessandro Moreschi who lived from 1858 to 1922 - Clapton has written a book about him - and the exhibition includes a recording of his done in 1902, the only surviving recording of a castrato.
The exhibition runs until October 1.
A recording of Alessandro Moreschi singing Ave Maria in 1904 is available to download free from the Internet Archive: http://www.archive.org/details/AlessandroMoreschi
Handel House Museum: http://www.handelhouse.org/