Frasier (Kelsey Grammer) makes a reference to his early suicide attempt, which was seen in the Cheers (1982) episode "The Girl in the Plastic Bubble"
When Frasier greets his brother at Cafe Nervosa, he turns from his book and says, "What fresh hell is this?", which is how writer Dorothy Parker used to answer her telephone.
The title card "The best laid plans..." was from poet Robert Burns' Of Mice and Men. The year before in The Simpsons (1989) episode Black Widower, Sideshow Bob who is voiced by Kelsey Grammer, misquoted that same line.
When Frasier (Kelsey Grammer) sits down to read his book (The Holotropic Mind by Stanislav Grof) he hums the "Toreador Song" from Georges Bizet's Carmen.
The celebrity caller in this episode is Christopher Reeve as Leonard. The plot in this episode is about Frasier seeking solitude. Superman had a Fortress of Solitude.