The biggest gathering of Pop Art pioneers since the Sixties met for the opening of the first exhibition devoted to their portraits.

Sir Peter Blake, Richard Hamilton, Joe Tilson and half a dozen more were guests of honour at a dinner marking the show at the National Portrait Gallery.

It includes more than 50 works by 28 American and British artists such as Andy Warhol, Jasper Johns, Allen Jones and Robert Rauschenberg.

A highlight is an entire section devoted to images of Marilyn Monroe. It includes works by artists including Warhol that were originally shown in the celebrated Homage To Marilyn Monroe at the Sydney Janis Gallery in New York in 1967.

Paul Moorhouse, curator of the show, Pop Art Portraits, said: "It's incredible. Some of these people knew each other as friends, some were rivals and some are meeting for the first time. The big thrill is that international figures such as [the American] Mel Ramos have come across to join forces with the likes of Allen Jones, Peter Blake and Richard Hamilton."

Sandy Nairne, director of the gallery, said the show was an exciting opportunity to see the movement in a new light.

The exhibition, sponsored by Lehman Brothers, opens tomorrow and runs until 20 January next year.