First, the blackface. John Howard Griffin's 1961 bestseller Black Like Me was derived from a series he did for Sepia magazine. Griffin took the drug Oxsoralen and sun-lamp treatments to give himself the illusion of being a black person. That such a treatment created only the illusion of being black was understood at the time.

Black Like Me was known enough that Eddie Murphy could parody it on a well-known Saturday Night Live sketch. Griffin's feat or stunt is re-created by Robert Downey Jr. as Australian actor Kirk Lazarus, who undergoes a controversial temporary chemical makeup. This dangerous comic bit informs Tropic Thunder's thesis: the more vainglorious an actor is, the more likely he is to be a donkey.

Everyone looks better in black, though. As in the standard Vietnam movie (especially Hamburger Hill), Downey's "Sgt. Osiris" is always the smartest, the most resourceful and the most well-spoken member of the cast. Since Lazarus is a method actor, he doesn't break character. ("I don't come out of character until the DVD commentary.") It's a performance, not a shtick. Thus the seeming blackface of this role is far closer on the scale to Olivier's Othello than it is to Al Jolson's Jazz Singer. (And Brandon T. Johnson, as Tropic Thunder cast member and rapper Alpa Chino, slaps Lazarus around for the pose.)

Director Ben Stiller plays Tugg Speedman, an action star best known for an endless series of sci-fi adventures (tag line: "Here We Go Again"); he's still smarting from the terrible reception of his indie eyesore Simple Jack, a corn-pone version of I Am Sam. His new film Tropic Thunder is going over budget because the actors are grandstanding one another. The source book's author, a gravel-voiced Vietnam vet (Nick Nolte), thinks he can guide the cast into the jungle for a small-camera guerrilla war movie. There, the helpless actors wander in the jungle and stumble into the lair of the Flaming Dragon, a mob of heroin manufacturers led by a child general (Brandon Soo Hoo).

As the cast goes missing, the film's profane and horrible producer video-conferences in threats; he's played by Tom Cruise, bald and matted with body hair like a chimp. Tropic Thunder's comedy is in explosive gags and inventive and quotable bits. Stiller and co-story writer Justin Theroux's story is often a knowing comedy about show-business excess.

In asides, we learn about the film that was the winner of the Crying Monkey Award at the Beijing Film Festival, or Lazarus's quotable explanation of why Sean Penn didn't win an Oscar for I Am Sam. There are times, especially in Osiris's mutterings, that Tropic Thunder seems as inspired as a Firesign Theater routine.

In the end, it spirals out into an action movie as even war movie parodies will. There are too many characters to keep track of, let alone redeem. Despite a memorable bit about a bat, Jack Black gets lost in the shuffle. And though the violence has the right balance with comedy--as opposed to the out-of-balance Pineapple Express--the movie is yet another boy's club. In the old days, even the war movies had actresses in them. The film's invention is remarkable, and Tropic Thunder is as close to the age of great screwball comedy as Ben Stiller has ever gotten.

TROPIC THUNDER (R; 107 min.), directed by Ben Stiller, written by Stiller, Justin Theroux and Etan Cohen, photographed by John Toll and starring Stiller, Jack Black, Tom Cruise, Robert Downey, Jr. and Nick Nolte, plays countywide.

Send a letter to the editor about this story.