By all accounts Karl Malden and Michael Douglas developed a strong professional and personal relationship from their time on the series. Twenty years after last working together on an episode they were both onstage at the 1996 People's Choice Awards. Malden referred to Douglas as "the son I never had" and mentioned that he had wanted producer Quinn Martin to cast Douglas on the series. Douglas responded to the compliment by calling Malden "my mentor," and both also expressed that they enjoyed working together on the show.
In order for Karl Malden to star on the series, Quinn Martin hired Michael Douglas for the role of Inspector Steve Keller, through Douglas' real-life father, Kirk.
Unlike subsequent generations of television production, the show made an effort to insinuate itself as seamlessly as possible into the fabric of the city. The series was filmed almost entirely on location in San Francisco. A warehouse converted to an interior scenes sound stage was located at the dead end of Kearny Street below Telegraph Hill, across from 1855 Kearny Street currently adjoined to 150 Chestnut Street, where it still stands today.
In West Germany, Steve was named "Heller", because there was already a "Kommissar Keller" (Erik Ode) on West German television.