Ever since he played baroque flute on Christopher Hogwood's first period-instrument recordings some 30 years ago, British-born conductor Nicholas McGegan has become known for excellence in authentic early music performance. What is it like for the director of the Philharmonia Baroque Orchestra and the International Handel Festival-Göttingen, the oldest Baroque music festival in the world, to conduct Handel's Messiah with a modern-instrument orchestra, as he will do this month with 33 Musicians of the Philharmonic and the Westminster Symphonic Choir?

"Musicians are musicians, and good musicians are good musicians," Mr. McGegan says. "Messiah is not an unfamiliar piece to almost any musician. Whether they play modern instruments or period instruments really doesn't make very much difference; I don't change my performance.

"Twenty, thirty, or forty years ago," he continues, "nobody cared how Handel did Messiah; it was about how 'we' do it. Whether or not you used original instruments didn't make any difference. There's now a good deal of research into the scale of performance in Handel's day, the speed, whether or not they sang ornament‹all that sort of thing. Music has acquired a historical conscience, if you will."

Research reveals that Handel performed Messiah only in theaters whose acoustics were less reverberant than those of Riverside Church. To compensate, Mr. McGegan will adopt slower tempos than he normally uses in the concert hall. "You can't use your knowledge of how Handel did Messiah dogmatically; you've got to bring it down to the practical. I'm much more interested in whether the words come across, because ultimately that's what it's about. If I were doing Messiah in Riverside with the full Philharmonic plus a chorus of 600 rather than with a reduced orchestra, it would be completely different again.

"There is an authenticity that exists in a performance," Mr. McGegan concludes, "and that is 'Does it get its message across?' It has nothing to do with what edition you used, whether you played period instruments, or engaged a countertenor instead of an alto. In other words, was the audience moved by that performance? Did Handel pluck your heartstrings? If the answer to that is 'yes,' we did well."

Jason Victor Serinus writes for Opera News, andante.com, Gay City News, and www.hometheaterhifi.com.