Gene Hackman had a rather abrasive relationship with Melvyn Douglas, who had wanted another actor to take the role of the son. Hackman never found out who this was, but said he used the estrangement between Douglas and himself to influence the playing of their scenes together.
Estelle Parsons plays Gene Hackman's sister, having teamed with him in 'Bonnie and Clyde' where she played his wife.
Richard Widmark was playwright Robert Anderson's first choice for the son role in both the theatrical and film versions of the play. One proposal had Fredric March as the father, another had it as a TV special with Spencer Tracy and Katharine Hepburn as the parents.
Edward G Robinson had been the original choice for the Melvyn Douglas role.