Due to the film's popularity and a claim, the film almost led to a spin-off Disney Afternoon TV series in 1989, which would've made this film the first to inspire a television spin-off - Disney Afternoon or otherwise. Instead, when the feature animation department green-lit Bernardo y Bianca en Cangurolandia (1990), the spin-off was reworked into the Disney Afternoon's Chip y Dale al rescate (1989), with Chip and Dale replacing Bernard and Miss Bianca.
One of Miss Bianca's traits, as portrayed in the original novel, was her trust and affection for felines (widely known as menacing predators of mice). This element was brought into the film in the form of Rufus the cat. Though he frightens the mice duo initially, he quickly shows he is a friend and is willing to help the mice on their quest to find Penny, with whom he shared a special friendship.
In the scene where Penny is seen carrying Rufus the cat off to supper, Penny grabs Rufus and uncomfortably carries him off in her arms, pushing him up with her knee as he begins to slip. Ollie Johnston, who animated this scene, explained that he did this in order to show the tender affection between Penny and Rufus, by having the cat be too fond of Penny to complain, since it would have been easier for Penny to walk away and have Rufus follow her.
While working on the film, Don Bluth noted that some of the characters did not have the whites of their eyes colored in. When he questioned the reason why, he was told that it was too expensive. Bluth and fellow animator Gary Goldman got their own equipment to test if it was true, they found that it was not too expensive. When they reported back with their discovery, the two were told to follow orders and do as they were told. Bluth referred to this as "the straw that broke the camel's back" which would eventually lead to Bluth and Goldman leaving Disney.
Considered by its producers, critics and audiences to be the film that proved that Walt Disney Productions' animation department would survive following the death of Walt Disney. It was the company's first major critical and financial success since El libro de la selva (1967), and its last until La sirenita (1989). Despite its high budget (for the time period), the film proved a huge success, managing to out-gross strong competition, such as La guerra de las galaxias (1977), in several European countries, including France and West Germany.