"Uptown Saturday Night" is essentially a put-on, but it's so full of good humor and, when the humor goes flat, of such high spirits that it reduces movie criticism to the status of a most nonessential craft.

The star as well as director of "Uptown Saturday Night" is Sidney Poitier, a man whose way with comedy is reminiscent of Stanley Kramer's in "It's a Mad, Mad, Mad, Mad World." It's less instinctive than acquisitive. He himself can't make anyone laugh but he knows people who can. Mr. Poitier has had the good sense to hire a lot of exceptionally talented and funny people, including Richard Wesley, who wrote the screenplay for "Uptown Saturday Night."

The film combines blunt, rollicking observations on life—the kind favored by black comedians—with the sort of fabulous narrative that has always been a staple of American comedy, from today's Woody Allen back...