Harlequins have signed Crusaders pair Mark Bryant and Michael Witt on two-year and three-year deals respectively.
Australian prop Bryant, 30, has been ever-present for the Welsh side during their three years in Super League.
Fellow Australian Witt, 27, scored 117 points in just 17 appearances in 2010 before a knee injury ruled him out.
Harlequins head coach Rob Powell said: "Mark is a top-quality, experienced prop. Michael will provide us with direction around the park."
He added: "[Witt] has a fantastic kicking game and is a great footballer. He will complement our existing quality play makers.
"[Bryant] has been a consistent performer in Super League over the last three years and will bring us experience and leadership."
Crusaders announced last month that they would not be competing in Super League in 2012 and club chief Rod Findlay has pleaded with other Super League sides to sign their players for next season.