They played cards together. She made a cameo in the ultimate Rat Pack movie, 1960's "Ocean's Eleven." And Sinatra and Martin weren't above pulling pranks on MacLaine, especially during the filming of William Wyler's 1961 drama "The Children's Hour."
"Dean and Frank used to come on the set and throw spitballs in a very dramatic scene that Audrey Hepburn and I were doing," MacLaine recalled recently. "They knew how to throw the spitballs without catching the light. There is one that is actually in the film."
MacLaine developed the same kind of playful friendship with Christopher Plummer while they were on location in New Orleans for their indie romantic comedy "Elsa & Fred," which opens Friday.
"We went to dinner every night," MacLaine said. "We experienced the New Orleans food, which we decided after one week all tasted the same. We got into different kinds of wine. He taught me about the wines."
"Elsa & Fred," she said, was a tough shoot because of the fast schedule and low budget. Her friendship with Plummer "made everything better than bearable."
After making movies for six decades, the 80-year-old Oscar winner ("Terms of Endearment") remains fit and funny. She lives primarily in Santa Fe, N.M., with her four rat terriers. "I'm very low maintenance," she said, laughing.
While most actresses over age 40 lament the lack of good roles, MacLaine is still in demand, whether it be guest starring on "Downton Abbey" or "Glee" or earning acclaim for her starring roles in such films as Richard Linklater's 2011 "Bernie."
"Elsa & Fred," directed and co-written by Michael Radford ("Il Postino"), seems made for MacLaine's offbeat sensibilities. She plays an eccentric, charming woman who embellishes the truth. Obsessed with Federico Fellini's 1960 masterpiece "La Dolce Vita," she yearns to re-create the famous scene with Anita Ekberg and Marcello Mastroianni at the Trevi Fountain in Rome.
Elsa is immediately attracted to Fred, a recent widower and first-class curmudgeon who has moved into the condo next door. The fanciful Elsa thinks Fred may be the man to make her dream come true. She brings him out of his shell, and they fall in love. When Fred learns that Elsa is harboring a secret about herself, he whisks her off to Italy.
"There was a real chemistry between the two of them," Radford said. "There was a screen connection between the two of them. Even, if you like, in the twilight of their careers, they are both still very glamorous people."
"Elsa & Fred" is based on a 2005 Argentine film "Elsa y Fred."
"It was a big hit in South America and not anywhere else, really," Radford said, adding that the film was a touch simplistic. "I thought we could make it a little bit more sophisticated and, with two great actors, turn it into something that really played. I saw the potential in it. It was right in my wheelhouse, in a sense that it was funny and sad."
MacLaine had her differences with Radford on the set.
"He's an English intellectual who grew up in colonial Africa," she said, adding that Elsa was a complicated character and that "we sometimes had our differences on how to play her."
The Oscar-nominated Radford said of MacLaine: "She is an incredibly intelligent woman and really good company, but on the set, I had to prove my worth."
Now that the film is heading into theaters, MacLaine said she's worried "Elsa & Fred" won't register at the box office.
"Let me ask you a question," MacLaine said. "If this doesn't work, will nobody invest in a story about old people's love and romance? We are underserved. People my age don't have anything to go to."
"I hope I can be the queen of the AARP."