The dog who portrayed Freeway was found in an animal shelter and was named "Charlie Gray". On the set he was especially close to Stefanie Powers. His offspring would portray "Junior" in the later Hart movies.
Sidney Sheldon had originally written a script for CBS called "Double Twist" about a married couple who were also both spies. Aaron Spelling and 'Leonard Goldberg' decided to update the idea for a potential television series. They asked Tom Mankiewicz to update the script, to make it more contemporary and viable for a potential weekly series. Mankiewicz reworked Sheldon's original script and it was renamed "Hart To Hart". Mankiewicz also made his directorial debut with the pilot episode as planned, and remained a "Creative Consultant" on the series.
In the episode "A Change of Hart", the Hart address is listed as 3100 Willow Pond Dr. Bel Air, CA 29042. However, that zip code is actually located in Denmark, SC. In the episode "Always, Elizabeth", the Hart's address is listed as 3100 Willow Pond Dr. Beverly Hills, CA 90047.