Episode "The Professionals: Klansmen (#1.13)" (1977), in which black people are harassed by a group that has modelled itself on the Ku Klux Klan, was banned and never shown in the UK because of its racial content.
In the series, all CI5 agents used numerical radio call signs. Bodie was Three-Seven, and Doyle Four-Five.
For many years actor Martin Shaw (Doyle) blocked repeat TV showings of the series, disowning it almost immediately after it had finished. Although he gave his reason as not being able to negotiate fees for TV repeats with programme makers London Weekend Television, it was also alleged that he didn't want to be typecast with the "hard man" image the show portrayed him to have. He only eventually relented to repeat showings in the mid-1990s when it was discreetly pointed out to him that the widow of Gordon Jackson (Cowley) could do with the income generated by repeat fees.
Original choices for the lead roles were Clive Revill (Cowley), Jon Finch (Doyle) and Anthony Andrews (Bodie). Andrews had already completed three days filming when he was replaced.