Laryngitis

Laryngitis was the inflammation of the larynx.

While making repairs to K9's brain circuit, the Fourth Doctor was surprised to find that K9 had contracted laryngitis. It caused K9 to speak with a hoarse, strained voice. He was at first left aboard the TARDIS to recover, (TV: Destiny of the Daleks, City of Death) but as he had not recovered over the course of a longer period, he was instead taken along on the adventures the Doctor and Romana II had. (TV: The Creature from the Pit - Shada) K9 eventually recovered. (TV: The Leisure Hive)

Melanie Bush was suffering from laryngitis when she helped the Sixth Doctor track down an alien insect. (PROSE: The Eyes Have It)

Behind the scenes

 * In Destiny K9 only appeared very briefly. Roy Skelton provided his voice in this story as he was only required a croaking cough. He was absent from City. K9 later appeared again from The Creature to Nimon and the unfinished Shada in which David Brierley provided his voice. John Leeson later returned as his normal voice from Leisure onwards.