LONDON — When the Chicago Lyric Opera approached the company controlling rights for Rodgers and Hammerstein musicals about staging their Big Five works, it might have quietly made history. By blurring the lines even further in a major opera company repertoire, the move hints at a turning point in how opera companies and symphonies stage American musicals alongside traditional blood-and-guts opera.

As opera houses search for new works and new audiences — and, ultimately, new sources of income and guaranteed ticket sales — musicals may be a salvation and, most likely, a staple of future repertoires. Musicals are drawing in audiences who have never attended a traditional opera — 50 percent of the audience at the recent Lyric Opera production of “Oklahoma!” were seeing their first production at the opera house — but also drawing the most jaded of opera-goers and symphony subscribers weary of yet another “Don Giovanni” or Beethoven’s Fifth.

“The vast majority of musicals are not appropriate to opera companies, but there are a small number of titles that are enhanced by the skill and scale of an opera house,” said Anthony Freud, general director of Lyric Opera of Chicago. “I see it as an inherent part of our output. I don’t see doing ‘The Sound of Music’ with any less professionalism than in doing ‘La Traviata.”’

The Lyric Opera is staging the Big Five — “Oklahoma!,” “The Sound of Music,” “Carousel,” “The King and I” and “South Pacific” — over five seasons, the first time the Rodgers and Hammerstein company has given such approval to an opera company.