Seymour is a deeply sensitive World War II veteran staying at a luxurious Florida beach resort with his wife. Haunted by his wartime experiences, he struggles to readjust to civilian life and the materialistic society around him. He spends his days isolating himself on the beach, stubbornly wearing a bathrobe to conceal himself, and finds his only sense of peace in the innocent company of young children.

Muriel is Seymour's young, well-to-do wife of five years. She is highly focused on fashion, socializing, and the resort's status hierarchy. While she is aware of her husband's deteriorating mental state following the war, she brushes off her family's concerns and maintains a detached attitude toward his struggles.

Sybil is a delicate, four-year-old girl vacationing at the Florida resort in a canary-yellow bathing suit. Unburdened by adult social conventions or materialistic concerns, she approaches the world with raw curiosity. She possesses a whimsical imagination and easily accepts Seymour's unusual stories about bananafish.

Muriel's mother is a protective and highly anxious woman who monitors the couple from afar. She is deeply disturbed by Seymour's recent behavior and fears for her daughter's safety. Despite her serious worries, she easily gets sidetracked by conversations about clothing and high-society gossip.

Mrs. Carpenter is Sybil's mother, a woman who is more absorbed in her own social life and leisure than in supervising her child. She quickly dismisses Sybil to play unsupervised so she can enjoy a martini and chat with her friend.

A guest at the Florida resort who spends time drinking martinis and chatting with Mrs. Carpenter.

A young girl staying at the resort. She earns Seymour's approval because she does not tease or poke the hotel dogs, though her presence frustrates Sybil.

Muriel's father is briefly discussed as the owner of the car that Seymour deliberately crashed into a tree. He consulted with doctors regarding his son-in-law's psychological state.