 Filmation originally produced 18 episodes for its network run, with  all the cast participating. When Filmation wanted to produce 6 more  episodes for a syndication package, some of the cast, including  Barry Williams (I) (qv) (Greg Brady), decided not to participate.  According to Williams in his book "Growing Up Brady", the cast read  word lists into a tape recorder and their lines were assembled from  these lists, probably with other voice talent filling in a line  where needed.