The first radio series (first six episodes) was broadcast on BBC Radio 4 in March and April 1978. A seventh episode was broadcast on 24 December 1978. This seventh episode was commonly known as the Christmas Episode. This had nothing to do with Christmas except in an early draft (which would have had Marvin the Paranoid Android as the "star" that was followed by the Three Wise Men); it was called the Christmas Episode because it was first broadcast on Christmas Eve.