Tonight the University of Hong Kong's Department of Music will present a version of George Frideric Handel's Messiah with a difference - orchestration by Wolfgang Amadeus Mozart. This interpretation of the work has been largely neglected in recent years, says Michael Ryan, who is directing the oratorio. 'People have been very keen on doing Handel the way Handel wanted it, and the trouble with this is it falls into the cracks. Is it Mozart or is it Handel? It's a bit of both, really, and that also makes it interesting,' he says. 'For the past 20 or 30 years there has been a lot of original instruments stuff and it is beginning to wear a bit thin. People are going back to playing Bach on the piano again, and doing things that are 'inauthentic'. The pendulum is swinging back again to something more creative - ideas going into performances.' Ryan's idea for this performance is also unusual in Hong Kong - a 'sing in' in which five choirs will participate under his baton, supported by a chorus who will rehearse this afternoon, hours before the actual performance. Anybody who has sung the work before - and, ideally, who has a copy of the score - is welcome to participate, organisers say. 'The idea is to drag along the score,' says Ryan, a part-time lecturer with the University of Hong Kong's music department. 'We'll rehearse in the afternoon, break for tea and then we'll do it.' Other voices will be supplied by the University of Hong Kong Chamber Choir, the City University of Hong Kong Staff Association Singing Group, the Hong Kong Bach Choir, the Hong Kong Oratorio Society and the Pro-Musica Society of Hong Kong. Solos will be sung by sopranos Chen Ti-wei and Chiffon Lee, tenor Felix Suen and baritone Sylvester Che, and the Mozart orchestrations will be played by members of the Hong Kong Chamber Orchestra. 'I don't recall this version being performed in Hong Kong before,' Ryan says. 'It's already sounding quite good. The student part of the chorus is doing very well - they're bright kids. The audience will stand up for the Hallelujah Chorus - they always do that - and we hope a few of them will join in.' It is possible to infer from Mozart's adaptation of Messiah that he might not have thought much of 'original instrument'-based performances of his own music. Handel composed Messiah in 1741 and this version was translated into German and first performed in 1789. Tonight's performance will be in English, however, and the instrumentation is right up to date, organisers say. 'The orchestral forces were increased to become those of the typical classical orchestra, the orchestra of Mozart's operas,' Ryan says. 'He did, though, allow quite a bit of Handel's original music to stand without alteration. 'Mozart gave the alto solos to a second soprano, or possibly a mezzo, and set a lot of the florid passages in the Part One choruses for the soloists, with the choir joining in the simpler passages. For parts Two and Three, the choruses are as in Handel's original.' Mozart left most of the solo parts unaltered, apart from shortening one aria, Why Do the Nations, and, for reasons unknown, dropping another, If God be for Us, altogether and substituting an original recitativo accompagnato for soprano. 'The main contribution from Mozart was the enhancement of the orchestral colour,' Ryan says. 'This has been rather unfashionable in recent years with the focus on 'original instruments', 'authenticity', and 'historically informed performance'. 'Mozart recognised the inherent quality of Handel's music but presented it to his peers through the prism of classicism. This view also deserves our attention.' Mozart's Messiah, tonight, 7.30pm, Loke Yew Hall, University of Hong Kong. Admission is free, but those wishing to attend are advised to register via the university's website www.hku.hk/music/concerts . Would-be chorus participants should be at the venue at 3.30pm. A limited number of chorus parts will be available for a nominal charge.