Scheduled opposite another teenage mystery-solving show, ABC's "The Hardy Boys", "Scooby-Doo" became a ratings success, with Nielsen ratings reporting that as many as 65% of Saturday-morning audiences were tuned in to CBS when "Scooby-Doo" was being broadcast. The show was renewed for a second season in 1970, for which eight episodes were produced. Seven of the second-season episodes featured chase sequences set to bubblegum pop songs recorded by Austin Roberts, who also re-recorded the theme song for this season. With Stefanianna Christopherson having married and retired from voice acting, Heather North assumed the role of Daphne, and she continued to voice the character until 1997.