The episode music improved and changed during the course of the series, but got a significant boost in the 6th season, with the addition of Pete Rugolo (prominent in the credits). He was probably the one who updated the iconic theme, and really improved the music used in each episode, modernizing the "feel" of the show. He scored many TV shows, and has quite an interesting career, according to Wiki. He died in 2011 at age 95.

Looked him up and saw he scored the 1960 film Private Property (the film debut of Warren Oates), great film, and was recently released on Blu Ray, the first time it's ever been released on any home format.

I loved Warren...."Get outa my way I'm gonna earmark this ugly devil!" -The Rifleman- The Marshal.

I like both arrangements but I agree the season 6 theme helped to modernize the show for the '60s. It was upbeat and lively and a nice change for the final year.

I loved Warren...."Get outa my way I'm gonna earmark this ugly devil!" -The Rifleman- The Marshal.

He was one of the greats.

For most of the series, stock music was used, some of it probably left over from the early 1950s. If you watch the first few seasons of MR. ED, they use some of the same stock music from LITB.

Pete Rugolo was a classically trained composer who studied with the great French composer Darius Milhaud, then teaching in California. He was certainly a boon for LITB.

Particularly on the first few seasons, they liberally used stock music. You'd hear the same music on the 5th season of Burns and Allen. As they got into the later seasons they introduced new music, some that I haven't heard elsewhere. The sixth season was a major upgrade.

They also used the same stock music from Alfred Hitchcock Presents and Alfred Hitchcock Hour. It's funny hearing Beaver music in a whole different show.

I'm more familiar with Pete's music from the background music he did for The Fugitive and Thriller and for the Outer Limits (same music used on Fugitive). I'm one of those people who notices background music, recently started watching the Annie Oakley TV series and they use the same background music Adventures of Superman used during it's first season. Talk about weird, hearing Superman background music used on a western TV show.

You will also hear the same MCA background music used on Leave It To Beaver, GE Theater, Alfred Hitchcock and even in some Hanna Barbera cartoons of the late '50's.