Serial: R  Episode Nos. 72,73,74,75,76, and 77.  Title: The Chase

The Daleks are determined to destroy the Doctor once and for all, and to this end they send an execution squad after the TARDIS in their very own time machine with orders to pursue it no matter where it may go, be it a desert world,
the Empire State Building, a haunted house, or a jungle.  Where can the Doctor escape to when the Daleks can follow
him anywhere in eternity?

This story marks the departure of William Russell as Ian Chesterton and Jacqueline Hill as Barbara Wright, and the debut
of Peter Purves as Steven Taylor.

starring William Hartnell as Dr. Who, William Russell as Ian Chesterton, Jacqueline Hill as Barbara Wright,  Maureen O'Brien as Vicki, and Peter Purves as Steven Taylor.  Written by Terry Nation, Produced by Verity Lambert, Directed by Richard Martin.

Originally transmitted from 22 May 1965 to 26 May 1965 on BBC1.
 

Serial 7H.  Episode Nos. 676, 677, 678, and 679.  Title: Remembrance of the Daleks

The Doctor returns to London, 1963 and the Coal Hill School area where he finds alien activity being monitored by the RAF.
As he has expected, his old enemies the Daleks are in the area searching for something he left behind on his first visit.  To his
surprise, however, there are two factions of Daleks, and his plans for the device could be ruined by their civil war, to say
nothing of London and Earth....

starring Sylvester McCoy as the Doctor and Sophie Aldred as Ace.  Written by Ben Aaronovitch, Produced by John Nathan-Turner, Directed by Andrew Morgan.

Originally transmitted from 5 October 1988 to 26 October 1988 on BBC1.