Written by Louis Marks and directed by Mervyn Pinfield and Douglas Camfield, the serial was first broadcast on BBC1 in three weekly parts from 31 October to 14 November 1964.

When Marks was commissioned to write the script, he was inspired by Rachel Carson's 1962 environmental science book Silent Spring, the first major documentation on human impact on the environment.

The story was originally written and filmed as a four-part serial, but later reduced to three parts; the third and fourth episodes were cut down to form a faster-paced climax.

This is overheard by the local telephone operator Hilda Rowse (Rosemary Johnson) and her policeman husband Bert (Fred Ferris), who suspect something is wrong.

The Doctor, realising the toxic nature of DN6 and the probable contamination of Barbara, proposes they alert someone by hoisting up the giant telephone receiver, but they cannot make themselves heard.

The Doctor and his companions decide to attract attention by starting a fire, succeeding in manoeuvring an aerosol can into the flames of the Bunsen burner gas outlet.

The concept of the Doctor and his companions shrinking in size was initially proposed as the first story of the show's first season, written by C. E. Webber and entitled The Giants.

[3] After some rewrites, the serial was rejected by show creator Sydney Newman in June 1963 due to its technical complexity and lack of character development.

[4] The concept of The Giants was given to writer Robert Gould in mid-1963 to develop as the four-part fourth serial of the first season, but it was dropped by January 1964 due to scripting difficulties.

[6] The main narrative was inspired by Rachel Carson's 1962 environmental science book Silent Spring, the first major documentation on human impact on the environment.

[12] The show's regular cast—Hartnell, Russell, Hill, and Ford—filmed the sequences in which they appeared alongside giant props; the effect was achieved by recording the actors through glass and reflecting the object onto a half-silvered mirror.

[14] Due to Pinfield's other commitments, the fourth and final episode was directed by Douglas Camfield, who had worked as a production assistant to Waris Hussein during the show's first season.

In The Discontinuity Guide (1995), Paul Cornell, Martin Day, and Keith Topping described the serial as "a strange mix of ecological [science fiction] and 'cops and gangsters'", finding it "good fun, if a little unrepresentative of the series".

[2] In 2012, DVD Talk's John Sinnott felt that the serial was a "solid installment", but considered it strange that the main characters do not interact with the criminals.