Belfast's Lyric Theatre has received backing from actor Kenneth Branagh as it nears a crucial fundraising deadline.
Last year, US-based Kresge Foundation said it would donate £500,000 to the Lyric's rebuild if the theatre raised £800,000 by 30 June 2010.
With just four weeks to go, the theatre still has £150,000 left to raise.
Belfast-born Mr Branagh appealed for people to give the Lyric "the support that it truly deserves".
The actor, who plays the title role in the popular BBC detective series Wallander, said: "There is an enormous wealth of creative talent in Northern Ireland, and I have worked with many great actors, directors and writers throughout my career who learned their craft at the Lyric.
"Young artists need the creative and spiritual home which the Lyric provides - a crucible in which they can experiment, innovate, take risks, and push boundaries," he added.
"Cramped and run-down"
The Lyric's development director, Angela McCloskey, said she is "confident" that the target will be reached.
Since the funding campaign for the new building began in 2003, nearly £17.5 million has been raised.
The original theatre opened in 1951 and moved to premises on Ridgeway Street about 20 years later.
However, ongoing problems with the building and dated facilities led to a decision to close it.
Ms McCloskey said: "Backstage working conditions at the old Lyric were described as the worst in the UK; shows had to be cancelled due to flooding; front of house facilities were cramped and run-down, with poor disability access; and we couldn't accommodate the huge demand for training and workshops."
The new theatre is now under construction on the banks of the River Lagan, and due to open in Spring 2011.
Almost three times the size of the old theatre, the new building will have a 390 seat auditorium, a 150 seat studio theatre, a rehearsal room, extensive riverfront foyers and bar, backstage facilities and office accommodation.
The development has been designed by award-winning architects O'Donnell & Tuomey, and is a blend of brick, glass and steel.
Ballymena-born actor Liam Neeson, who got his start as an actor at the Lyric, has already thrown his weight behind the campaign.
In January he hosted a star-studded dinner in New York that raised nearly $400,000 (£273,482) for the theatre.