The difference between the parts is that Barbara, unlike Proof's Claire, is a screamer; she famously brings down the house at the Act Two curtain in the three-act darkly funny family drama by Tracy Letts. Amy Morton, who created the role and was Tony-nominated for her work, is leaving the Broadway production to re-create the part in the London premiere this fall. She exited Oct. 12.

Also joining the Broadway cast Oct. 14 are Michael Milligan as Little Charles, Dee Pelletier as Ivy Weston and Scott Jaeck as Sheriff Deon Gilbeau.

Best known for her Tony and Lucille Lortel award-nominated performance in Proof, Day most recently appeared in A Midsummer Night's Dream, directed by Lisa Peterson, at Hartford Stage. Her other notable theatre credits include Edward Albee's Peter and Jerry (Drama Desk nomination); Ethan Coen's Almost an Evening; The Evildoers by David Adjmi at Yale Rep; Leslie Ayvazian's Behave Yourself at the Adirondack Theatre Festival; Distracted at the Mark Taper Forum; Noah Haidle's Vigils at the Goodman Theatre; The Rainmaker (Helen Hayes Award) at Arena Stage, and more.

Juilliard-trained Milligan appeared Off-Broadway in Thom Pain and The Golem and has appeared regionally at McCarter Theater, Westport Playhouse, Studio Arena, The Shakespeare Theatre (D.C.), Cincinnati Playhouse, and the Alabama, Utah, New Jersey, Milwaukee, St. Louis and Colorado Shakespeare festivals.

Pelletier has been seen on the New York stage in Bug and Speaking in Tongues and in regional productions of The Price, The Syringa Tree, Hamlet and Hedda Gabler. Her screen credit include "Law & Order," "Law & Order: Criminal Intent" and "Third Watch." Jaeck has been seen on Broadway in Night of the Iguana and in regional productions at Chicago Shakespeare Theater, Goodman Theatre, Alliance Theatre, Pasadena Playhouse, Indianapolis Rep, Milwaukee Rep, Victory Gardens Theatre and Northlight Theatre. His screen credits include "The Lucky Ones" (to be released), "Washington Square," "Prison Break," "Charmed," "ER" and "Seinfeld."

Directed by Tony, Drama Desk and Outer Critics Circle Award winner Anna D. Shapiro, August: Osage County — at the Music Box on West 45th Street — is "the explosively funny comedy-drama focusing on the Weston family following the disappearance of the family's patriarch."

It won the 2008 Tony Award for Best Play and the 2008 Pulitzer Prize for Drama.

Tickets can be purchased at Telecharge.com or by calling (212) 239-6200.