The plot of the overinflated MGM musical Broadway Rhythm can be summed up briefly: Musical comedy producer Jonnie Demming (George Murphy) dismisses his vaudevillian dad Sam Demming (Charles Winninger) as old-fashioned. Jonnie signs Hollywood star Helen Hoyt (Ginny Simms) to a Broadway show, but she turns it down. Sam saves the day by dredging up an old script he'd done in summer stock-which, of course, Helen agrees to play. All of this can be forgotten, and in fact will be forgotten, once the film's parade of "guest stars" gets under way. Such stage and screen luminaries as Lena Horne, Ben Blue, Nancy Walker, Eddie "Rochester" Anderson, Hazel Scott and Tommy Dorsey & His Orchestra make up for the narrative banalities with such musical numbers as Gershwin's "Somebody Loves Me" and Jerome Kern's "All the Things You Are.""