Colin Baker makes his first full appearance as the Doctor in the final serial The Twin Dilemma.

Janet Fielding (Tegan Jovanka) and Mark Strickson (Vislor Turlough) continue their roles as the Fifth Doctor's companions for their final season, Janet Fielding leaves in Resurrection of the Daleks and Mark Strickson departs in Planet of Fire.

New companion Peri Brown played by Nicola Bryant makes her first appearance in Planet of Fire.

The shape-shifting Android Companion Kamelion, played by Gerald Flood, makes his second and final appearance in Planet of Fire, though the character itself – along with other Fifth Doctor companions who left by this story (Tegan, Nyssa, Adric, and Turlough) – all make illusionary cameos as the Doctor regenerates at the climax of The Caves of Androzani.

Transmission moved to Thursdays and Fridays, except for Resurrection of the Daleks which was aired in two double-length episodes on Wednesdays.