The Doctor brings Martha home, on the day after she joined him in the TARDIS. Almost immediately, she learns that her sister, Tish, has been working for the venerable Professor Lazarus, who has invented a machine which allows him to restore his own youth. But the Doctor knows that this kind of technology must have consequences -- consequences he may not be able to prevent, as agents of the enigmatic Mr Saxon begin to take an unhealthy interest in him.

Stephen Greenhorn had begun his writing career in radio and theatre before moving to television, where he worked on episodes of The Bill and Glasgow Kiss. Greenhorn then created the soap opera River City prior to landing scripting duties on the TV movie adaptation of Wide Sargasso Sea. Greenhorn's executive producer on the latter was BBC Wales Head of Drama Julie Gardner, who held the same post on Doctor Who, and Greenhorn expressed to her his desire to write for the Time Lord as well. In the spring of 2006, Greenhorn met first with Gardner and Doctor Who script editor Simon Winstone, and then with Doctor Who executive producer Russell T Davies, who confirmed that he wanted Greenhorn to write for the series.

Davies asked Greenhorn to develop an episode set on modern-day Earth involving a “mad scientist”. The pair thought especially in terms of the many scientific masterminds who had appeared in the Marvel line of superhero comic books, such as Spider-Man foes Doctor Octopus and the Green Goblin. Greenhorn also sought inspiration from tales of experiments gone horribly wrong featured in films such as The Fly and stories like Robert Louis Stevenson's The Strange Case Of Dr Jekyll And Mr Hyde.

Several of Greenhorn's initial ideas had to be discarded because they were too similar to concepts being developed either for the first season of Torchwood or (in the case of using the Thames Flood Barrier as a setting) the 2006 Doctor Who Christmas special The Runaway Bride. Another suggestion, that Greenhorn's scientist character be working on developing invulnerable synthetic skin, was dropped because Davies feared that this might be part of the plot of the movie Spider-Man 3, which was due for release in May 2007, around the same time that Greenhorn's episode would likely air. (As it turned out, the origins of the villainous Venom in that film hewed closer to its comic book roots as an alien parasite.)

Finally, however, Greenhorn hit upon the notion of an aged scientist trying to make himself young again. This character was first given the pulpish name Professor Anger, and subsequently became Professor Lazarus, after the man raised from the dead by Jesus Christ in the Gospel According To John. Accordingly, the episode gained the working title “The Madness Of Professor Lazarus”. Davies asked Greenhorn to make strong use of Martha's family in his script; of these, the writer especially cast the spotlight on Tish (whose full given name was originally revealed to be Patricia, then changed to Letitia). At a late stage, Davies added the material between Francine and the agents of Mr Saxon (whose first name, Harold, was mentioned for the first time), setting up elements which would pay off in the season finale The Sound Of Drums / Last Of The Time Lords.

The director assigned to both “The Madness Of Professor Lazarus” and Gridlock (which together formed Block Three of the production schedule) was Richard Clark. Headlining his cast was Mark Gatiss as Lazarus: a renowned actor with the comedy troupe The League Of Gentlemen, Gatiss had also written both The Unquiet Dead and The Idiot's Lantern for Doctor Who's first two seasons. A major location in Greenhorn's storyline was St Paul's Cathedral in London, which could be viewed from Lazarus' office. Arrangements were made to film material at St Paul's itself, only for these to fall through shortly before recording was to commence. Consequently, Greenhorn was forced to hastily alter several elements of the script, relocating the action to London's Southwark Cathedral instead.

The location actually used as Southwark, however, was Wells Cathedral in Wells, Somerset, where filming took place on October 3rd and 4th, 2006. Action then shifted to the Senedd, home of the National Assembly for Wales in Cardiff. This was the setting for Lazarus' reception, and recording occurred there on October 5th and 6th, and from the 9th to the 12th. Part of October 11th was also spent at Churchill House in Cardiff, for Lazarus' rooftop metamorphosis. The 13th saw cast and crew move to Lloyds TSB in Cardiff; this provided Lazarus' office, and the shot of him dying in Southwark Cathedral was captured there as well.

On October 16th, the Cardiff National Museum was the venue for Lazarus' press conference, the foyer of his laboratory, and the security station; the exterior scene in which Francine slaps the Doctor was also taped there. The final piece of location work was completed on the 17th at Cardiff University's Biomedical Science Building, serving as Lazarus' lab itself. The same day, studio recording began at Upper Boat; this primarily concerned greenscreen work and inserts, which continued to the 18th. Material in Martha's flat and inside the Genetic Manipulation Device was filmed on October 19th; scenes inside the TARDIS were planned for this day as well, but in the event these were delayed until November 7th, together with further inserts.

In December, Davies decided to truncate the episode's title to The Lazarus Experiment. Although this appeared to echo Nigel Kneale's quintessential 1953 science-fiction serial The Quatermass Experiment -- especially since David Tennant and Mark Gatiss had costarred in a live remake of the story for BBC Four in 2005 -- Davies insisted that this was not intentional.

• Outpost Gallifrey: New Doctor Who Series News Page, edited by Shaun Lyon.
• Doctor Who Magazine Special Edition #17, 22nd November 2007, “Episode 6: The Lazarus Experiment” by Andrew Pixley, Panini Publishing Ltd.