The main characters are two bananas named B1 and B2. Other characters include three Teddy Bears named Amy, Lulu and Morgan, and Rat in a Hat. The Bananas, the Teddies and Rat in a Hat all live in the same neighbourhood, a cul-de-sac called "Cuddles Avenue" at the end of a street.
The Bananas are noted for their common catchphrase, often said when the duo get an idea: "Are you thinking what I'm thinking, B1?" "I think I am, B2!". Rat in a Hat also has two catch phrases - "Oh, Cheese and Whiskers!", usually stated when he has not succeeded at a task; and "I'm a rat, I'm a rat, I'm a clever clever rat", which he sings when he thinks of a good idea.
The characters were inspired by a 1967 song written for children by British composer Carey Blyton (nephew of renowned children's author Enid Blyton). The jaunty song describes (an unspecified number of) bananas in pyjamas chasing teddy bears, with a slight twist at the end where a musical sting emphasises that the bananas like to "catch them unawares". The lyrics for the song seem to be inspired by the 1932 John Bratton song "Teddy Bear Picnic." Teddy Bear Picnic lyrics & Bananas in Pajamas lyrics]
The song was shown on the Australian version of Play School for many years accompanied by an animation depicting pairs of bananas in blue-and-white striped pyjamas. This led to a "Banana" plush toy being created as part of the 'toy cast', which formed the basis of the physical appearance of B1 and B2.
Given the age of the target audience, chasing teddy bears is not usually a plotline for the show itself, and when it is depicted, it is usually in a playful manner. More often, the bananas engage in activities in singing, dancing, and playing with the other characters, and bantering with each other.
The show was performed using human actors in elaborate costumes, in the style of the British Teletubbies or Tweenies. In the show's early days, the voices of the bananas were provided by the same actors as were inside the costume, but the original actors eventually gave up that aspect of the show and substitutes manned the hot, stuffy costumes. The show aired new episodes from its 1992 debut to its eventual run in syndication in 2000. The show aired 299 episodes and 4 specials. Its debut in the United States was in 1995. It made videos and other media from 1995 to 1999. A toy line, developed by TOMY, debuted in 1996.