One of the reserved spaces in the hotel parking lot (at 22:02) is for country singer, Glen Campbell.
The building used (the Riviera country club) as the hotel was also used as the West End Tennis Club, in The Kirkoff Case (1974)
Dennis makes reference to the pearl switch, in the episode, Counter Gambit (1975). Eric Server, who played the banking representative William McKenzie, appeared on that episode, as Moss' attorney, Kramer.
The gruff voice of Tony on the opening's answering machine message is that of Eddie Fontaine, who appears in this, and several other episodes.