When the pilot episode for "Bonanza" was originally run, it included the four Cartwrights singing the words to the theme song. The audience reaction was generally to role on the floor laughing, as the words were comical and the picture of these cowboys jumping on their horses singing them rediculous.
For the rest of the series the familiar instrumental version of the song was used, and it's even heard in the re-runs of the pilot "A Rose for Lotta".
So for those who have never heard the lyrics to "Bonanza" (although Lorne Greene sings it on several of his records!), here they are:

Bonanza

We chased lady luck, 'til we finally struck
Bonanza
With a gun and a rope and a hat full of hope,
we planted our family tree.
We got a hold of a pot full of gold,
Bonanza
With a horse and a saddle, and a ring full of cattle,
How rich can a fellow be?
On this land we put our brand, Cartwright is the name,
Fortune smiled, the day we filed the Ponderosa claim.
Here in the west, we're livin' in the best
Bonanza
If anyone fights any one of us,
he�s got a fight with me
Bonanza
Hoss and Joe and Adam know every rock and pine,
No one works fights, or eats, like those boys of mine
Here we stand in the middle of a grand
Bonanza
With a gun and a rope and a hat full of hope,
we planted our family tree.
We got a hold of a pot full of gold,
Bonanza
With a houseful of friends where the rainbow ends,
How rich can a fellow be?
On this land we put our brand Cartwright is the name,
Fortune smiled, the day we filed the Ponderosa claim.
Here in the west, we're livin' in the best
Bonanza
With the friendliest, fightingist, lovingist band,
That ever set foot in the promised land
And we're happier than them all.
That's why we call it
Bonanza... Bonanza... Bonanza.