When it comes to luring top guests, “Monk” has a secret weapon.

“I like to pretend it’s the writing that appeals to them,” says exec producer Andy Breckman, “but the truth is it’s the chance to work with Tony (Shalhoub). He’s an actors’ actor.”

Guests such as Stanley Tucci, John Turturro, Laurie Metcalf and David Strathairn signed on because they knew or had worked with the “Monk” lead.

“I never thought we’d have a chance at David Strathairn,” says showrunner Randy Zisk, but Strathairn recently played a genius battling wits with Shalhoub’s Adrian Monk. “John Turturro won an Emmy (playing Monk’s brother, Ambrose) and has now done three episodes — and he’s never done much television.”

After 100 episodes, actor interest remains strong.

“‘Monk,’ the series, may not be the newest, sexiest kid on the block, but it’s a really great show, and actors know that,” says “Monk” casting director Amy Britt.

Most guest roles are realistic. “With the exception of maybe Tim Bagley (as Monk nemesis Harold Krenshaw) or Sarah Silverman (as Monk’s top fan), there aren’t a lot of charactery people on the show,” notes casting associate Corbin Bronson.

The roles also tend to be one-offs, though Bagley and Jarrad Paul, as Monk’s neighbor, proved popular enough to be invited back whenever possible.

Finding the right actors isn’t always simple. Britt, Bronson and casting director Anya Colloff see between 100 and 200 actors in preparation for each episode.

“Oftentimes if Tony’s available, he’ll run over from set and read with actors,” Britt says. “It’s very evident if somebody can hold their own opposite him.”

“But he’s a producer (too), so it behooves him to do it,” Colloff adds. “He loves it, he has such a good time. He’s like, ‘I’ll sit and eat my lunch and read with actors. Whatever you need me to do.’ Which is great and very generous.”