Howard Shore ‎– The Fly OST (1986, CD)

"Cronenberg's collaboration with Howard Shore had been responsible to a great degree in bringing the composer from the anonymity of television and other writing venues into the motion picture scene, and their work together would continue for several decades. The two agreed to approach The Fly as though it were an opera, playing the tragedy very literally and melodramatically in the tone of the music. The technique would be relatively new in a genre that had been recently defined by far less traditional (or even orchestral) sounds, but it would prove to be successful due to the inherent emphasis on the romance in the story. The sound would also inform a new generation of film music in the genre, including the work of Christopher Young, whose score for the idiotic sequel to The Fly in 1989 would extend the larger-than-life scope of Shore's approach into another generation of fly mutation horror." via Filmtracks

This is an out of print [remastered] soundtrack to one of the greatest sci-fi horror films ever made. 

Here.