According to The Encyclopedia of TV Game Shows First Edition, the hosts of Concentration on NBC were Hugh Downs (August 1958 to January 1969), Jack Barry (1958 prime time), Bob Clayton (January–March 1969 and September 1969 to March 1973) and Ed McMahon (March–September 1969). Substitute hosts were Art James, Jim Lucas (both of whom had previously been Concentration announcers) and Bill Mazer.
Downs had other jobs with NBC while he was host of Concentration: He was the announcer for Jack Paar on The Tonight Show and an anchor on The Today Show. (In 1968, Downs won an Emmy® as the host of the daytime Concentration.) Gene Rayburn was Downs’ competitor at the host audition for Concentration, but would become more famous as the host of another NBC game show, The Match Game.
Jack Narz was the host of the syndicated Concentration, produced by the Goodson-Todman team. (He was working on another Goodson show, Now You See It, at the same time.)
In 1985, Goodson produced 10 Concentration pilots with Orson Bean as host. In these pilots, contestants played for cash, matching related words (such as TUNA and FISH, or JOHNNY CARSON and JOAN RIVERS) instead of prizes. The bonus round involved matching prizes instead of cars.
From 1987 to 1991, Alex Trebek was the host of Classic Concentration on NBC. In 1991, Trebek distinguished himself in his field by hosting three game shows at once: Jeopardy!, Classic Concentration and To Tell the Truth.