Pauley Perrette Reacts to 'NCIS' Reaching 300 Episodes: 'I Think It's the Greatest Show Ever'

This video is unavailable because we were unable to load a message from our sponsors.

If you are using ad-blocking software, please disable it and reload the page.

The stars of NCIS are reaching rare air this season, and they celebrated with ET.

The CBS drama airs its 300th episode on Tuesday, which puts them in an exclusive club that includes TV classics like CSI, Law & Order and ER. The number is such a huge accomplishment that even a veteran like Mark Harmon hasn't wrapped his mind around it yet.

WATCH: Why 'NCIS' is the No. 1 Show in the World

"I just know it's a lot," Harmon told ET. "It's a round number, so it's a lot."

On the other hand, actress Pauley Perrette saw this coming long ago.

"I'm like the biggest NCIS fan," Perrette admitted. "I think it's the greatest show ever."

Beyond the 300 episodes, NCIS is also the most popular TV drama in the world. The show is seen in more than 200 markets worldwide and dubbed and broadcasted in more than 60 different languages.

WATCH: 'NCIS' Cast Reflects on 250 Episodes

Still, the mile marker is bittersweet as the NCIS family will be losing one of their core members after this season. Michael Weatherly announced in January that he would be leaving the show after 13 seasons as Special Agent Tony DiNozzo. Harmon dished on how the team plans to fill that gaping hole.

"Our job here is to really move forward and to try to take the change and not so much replace as it is renew and find something new," Harmon said. "That's what we've been able to do for a while and we'll see if we can't keep doing it."