When Conan Visits Dave, the Topic Inevitably Is Jay

8:51 p.m. | Updated So what would David Letterman and Conan O’Brien talk about when the two late-night hosts got together for a chat Thursday night? The Indy 500?

Hardly. On Mr. O’Brien’s first appearance in 13 years as a guest on Mr. Letterman’s CBS show, the talk turned quickly to a subject they most have in common: Jay Leno.

Mr. O’Brien, after a time when the subject of his ouster from NBC’s “Tonight Show” seemed to dominate his every waking thought, has lately steered away from rehashing his unhappy departure from NBC.

But, inevitably, Mr. Letterman was going to use this opportunity to bring it up. The two men traded barbs about Mr. Leno on Thursday night, about how he would surely be watching the interview, and what kind of relationship Mr. O’Brien had with him, before and after the “Tonight Show” turnaround.

Mr. Letterman made an observation he has long made about Mr. Leno: that as a stand-up comic in the 1970s, he was “the guy.” But he told Mr. O’Brien that even then, Mr. Leno was “a bit of a brat.”

It wasn’t exactly a harsh charge, certainly not the worst Mr. Leno has heard from Mr. Letterman, but it underscored Mr. Letterman’s often-stated conviction that Mr. Leno’s character had never changed in all the years he had known him. (Later, Mr. Letterman called Mr. Leno a felon, then corrected himself to say “a felony took place.”)

Of course, the biggest thing the two comics have in common is that they both lost the “Tonight Show” to Mr. Leno, and the scar has apparently not healed for either of them.

Mr. Letterman also made reference to the period when Mr. O’Brien had his two-week confrontation with NBC over the decision to remove him, calling it “the golden age of television.” (That is, it provided Mr. Letterman with night after night of ferociously pointed comedy.) He said the situation had made him very happy, “except that you lost your job.”

Mr. O’Brien said his only consolation during that period was knowing Mr. Letterman was happy.