Included in the latest batch of star names to confirm their availability are former Lions James Hook, Dwayne Peel and Matthew Rees, All Blacks Joe Rokocoko and Nick Evans, four members of Italy's Six Nations team - Sergio Parisse, Martin Castrogiovanni, Leonardo Ghiraldini and Alessandro Zanni - and Springboks BJ Botha, Marco Wentzel and Francois Louw.
In all, ten different nationalities are represented, including two new flying wings, US Eagle Takudzwa Ngwenya and Hong Kong's Sevens skipper Rowan Varty plus Samoa's world class scrum half Kahn Fotuali'i.
In the best Barbarians' tradition, two uncapped players have been invited - Kiwi full-back Jared Payne, currently with Ulster after several seasons of Super Rugby with the Crusaders and Blues, and former England Under-20 flanker Sam Jones of London Wasps.
Team manager Derek Quinnell said: "Our selection process has taken several months and is still not quite complete. Over the next week or so we will be monitoring the domestic play-off matches in Europe and the various national squads for the summer tours.
"Also, one or two players in the squad announced today may not be available for both of our matches so we expect to add other significant names to the team in the near future.
"The Barbarians kick off their tour against England at Twickenham on Sunday, May 26 before flying to Hong Kong for the historic encounter with the British & Irish Lions on Saturday, June 1.
BARBARIANS SUMMER TOUR SQUAD (v England/British & Irish Lions):
Backs (9) -
Jared Payne (Ulster)
Rowan Varty (DeA Tigers/Hong Kong)
Takudzwa Ngwenya (Bairritz Olympique/USA)
Joe Rokocoko (Bayonne/New Zealand)
James Hook (Perpignan/Wales)
Kahn Fotuali'i (Ospreys/Samoa)
Dwayne Peel (Sale Sharks/Wales)
Dimitri Yachvili (Biarritz Olympique/France)
Forwards (13) -
Duncan Jones (Ospreys/Wales)
BJ Botha (Munster/South Africa)
Paul James (Bath/Wales)
Martin Castrogiovanni (Leicester Tigers/Italy)
Matthew Rees (Scarlets/Wales)
Leonardo Ghiraldini (Benetton Treviso/Italy)
Marco Wentzel (London Wasps/South Africa)
Jim Hamilton (Gloucester/Scotland)
Francois Louw (Bath/South Africa)
Sam Jones (London Wasps)
Alessandro Zanni (Benetton Treviso/Italy)
Sergio Parisse (Stade Francais/Italy)
Imanol Harinordoquy (Biarritz Olympique/France)
Coach: David Young
Player/assistant coach: Mike Tindall (Gloucester/England)