For years there were stories that Katharine Hepburn and Robert Mitchum didn't get along. One day she told him, "You know you can't act, and if you hadn't been good looking you would never have got a picture at all. I'm tired of working with people like you who have nothing to offer." However, Mitchum told Dick Cavett in a TV interview that this story is completely apocryphal as he and Hepburn got along famously.

MGM originally told Laraine Day that if she played the female lead in Keep Your Powder Dry (1945) it would reward her with the female lead in Undercurrent (1946). Although she kept her part of the bargain and appeared in that production, MGM failed to fulfill its promise and gave the lead to Katharine Hepburn. Day responded by asking and receiving a release from her MGM contract in 1946.

In Vincente Minnelli's autobiography, he says that Robert Mitchum was very uncomfortable in the role of the sensitive Michael.

Film debut of Jayne Meadows.

Alan drives a 1946 Lincoln Continental convertible. In San Francisco, the rental car Ann drives to the ranch is a 1942 Chrysler convertible.

This was Robert Taylor's first movie since returning from military service in World War II.

The airplane shown taking Ann and Alan to Washington, DC--flying mid-air--is an American Airlines Douglas DC-3 DST (Douglas Sleeper Transport), registration NC16001, named "Flagship New York". It was the first DST in service. It first flew with AA in 1936 and was impressed into USAAF service as a C-49E in WWII as reg. 42-56097. On December 18, 1943, it crash-landed at Biggs Army Airfield, Ft. Bliss, TX, and was scrapped. This same plane can be seen in Murder Over New York (1940).

This film was a hit at the box office, earning MGM a profit of $1,001,000 ($13.47M in 2017) according to studio records.

"Lux Radio Theater" broadcast a 60-minute radio adaptation of the movie on October 6, 1947, with Katharine Hepburn and Robert Taylor reprising their film roles.

"The Screen Guild Theater" broadcast a 30-minute radio adaptation of the movie on May 5, 1949, with Robert Taylor reprising his film role.

The plane shown landing in Washington, DC, is an American Airlines Douglas DC-3-277D, registration NC33651. In service with AA from 1941-49, it was named "Flagship Clarksburg" and was subsequently acquired by the Brazilian airline Varig and registered as PP-VDL. During a training flight on January 3, 1958, it crash-landed at Porto Alegre, Brazil. The damage was beyond repair and it was scrapped.

This film was first telecast in both Los Angeles and Seattle Wednesday 8 February 1957 on KTTV (Channel 11) and on KING (Channel 5); it first aired in Portland OR 16 March 1957 on KGW (Channel 8), in Norfolk VA 23 March 1957 on WTAR (Channel 3), in Syracuse NY 27 March 1957 on WHEN (Channel 8), in Minneapolis 28 March 1957 on KMGM (Channel 9), in Philadelphia 31 May 1957 on WFIL (Channel 6), in New York City 3 June 1957 on WCBS (Channel 2), in Altoona PA 14 June 1957 on WFBG (Channel 10), in Chicago 22 June 1957 on WBBM (Channel 2) and in Cincinnati 19 July 1957 on WXIX (Channel 19) (Newport KY); in San Francisco it was first seen 7 August 1959 on KGO.