"S.O.S." is a song Yū Aku and Shunichi Tokura wrote for Japanese idol duo Pink Lady. It was released as the group's second single in November 1976, and became their first number-one hit on the Japanese Oricon singles chart in the following year.

"S.O.S." features Morse code which stands for the song title at the opening of the song. Because its sound effect might be mistaken for genuine Morse code, intro of the track has been omitted occasionally when the song has played on the radio. The song has been one of favorites for both the duo and the fans, and it is also one of the essential songs performed in their concerts.

Led by commercial success of its predecessor "Pepper Keibu" which reached the number-4 on the Japanese Oricon chart, "S.O.S" climbed the top of the country's hit parade three months after its release. A single remained on the chart for 38 weeks, selling approximately 650,000 copies. According to the record label Victor, "S.O.S." has sold in excess of 1.2 million units to date.

According to Oricon it was the 8th best selling single from 1977.

A re-recorded version of the song was included on the 2-disc greatest hits release, Innovation, released in December 2010.

The song is used as background music in one episode of the anime television series His and Her Circumstances, as a song the female lead, Yukino Miyazawa, can't get out of her head.

All tracks composed by Shunichi Tokura, lyrics written by Yū Aku.

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