This is from an episode of the Brady Bunch Variety Hour, which I have to admit has become a bit of an obsession of mine ever since I discovered that the majority of the episodes have been uploaded to YouTube.
For those keeping track, Barry Williams was Greg. Maureen McCormick was Marcia. For the Variety Hour, Geri Reischl was Jan, replacing Eve Plumb. Despite rumors to the contrary, Plumb did originally agree to return as Jan but she balked at singing a long-term contract so Geri was hired instead. Geri is actually a pretty good singer. Certainly, she’s dramatically better than any of the original Brady kids.
Barry was also reluctant to return to the role of Greg Brady but he did so after he was assured that he would be the centerpiece of the show and that he would be given several songs to sing in each episode. Actually, the show’s producers kept their word because Barry was probably the most heavily featured of the Brady kids. (Unfortunately, Barry really didn’t have much of a singing voice.) As for Maureen, she has since written that she was struggling with cocaine addiction at the time and, hence, she doesn’t remember much about The Brady Bunch Variety Hour.