An unsubtle comedy of guys who refuse to grow up surprisingly grows on you, says Donald Clarke

MIGHT I be allowed a few moments' indulgence to argue that Step Brothers, in which Will Ferrell and John C Reilly play middle-aged 10-year-olds, is less of a broad comedy than a profound exercise in old-fashioned surrealism?

Think about it. The film finds the two unemployed losers being pressed together after Will's mom and Reilly's dad marry one another. Obsessed with loud rock music and big boobies, the two bicker like babies and take every opportunity to reveal their pathological immaturity.

Watch as Will rubs his testicles on John's drum kit. Laugh as teenage bullies beat the lads up. Yet the film, otherwise a standard, quasi-naturalistic Frat Pack affair, makes no serious attempt to acknowledge the leads' apparent learning difficulties. And what's all this with Mary Steenburgen (born 1953) playing the mother of Will Ferrell (born 1967)? It's just like a Buñuel film. Isn't it?

Well, no. Not really. Step Brothersis the latest movie from Adam McKay, the director of Anchorman and Talladega Nights, and, like those two fine entertainments, it rejoices in making a virtue of its own rampant stupidity.

Long used to playing childlike men, Ferrell is here offered the opportunity to boil his stock character down to its gibbering essence. Meanwhile, Reilly, who has recently found a way of using his crushed vulnerability for comic purposes, knocks together a character that conveys the coiled violence that lurks within many children.

In the course of the film they run through all the traumas of early adolescence and, exploiting the comedy of discordance to the full, make something fresh and amusing of every one. Both actors, aware that the film does have a point to make about modern men and their unwillingness to grow up, allow just enough middle-aged misery to creep in without tipping the film into total absurdity.

The key performances may, however, come from Richard Jenkins and Mary Steenburgen as the parents. All comic sketches require a stooge to stand by in bewilderment and make aghast comments at the antics of the principal comedian. Richard and Mary approach the task in variously effective ways. Whereas Steenburgen registers genuine sorrow at the boys' occasional crises - even shedding real tears at one point - Jenkins is the only person allowed to share the audience's bewilderment at the unfolding lunacy.

When the lads finally make friends, they rush into their folks' bedroom and propose turning their beds into bunks. This way, Will explains, they can do more "activities". Only Jenkins seems to realise the oddness of the situation. "You're adults, you can do what you want," he wails. The awareness that just one character knows the universe is out of kilter adds another layer of delightful absurdity to proceedings.

So rather than being a surreal masterpiece, Step Brothersis a classic of lowbrow humour? That analysis doesn't really hold up either.

It is a continuing frustration that the collaborations between Ferrell and McKay always look as if (appropriately for this project) they were written by two inattentive teenagers after happening upon their bigger brother's main stash. One feels the urge to storm into

the writers' heads and demand they tidy the place up a bit. Oh, you've left your denouement lying unattached in the middle of your cerebellum. What are these unresolved subplots doing curled around your synapses? I hope you don't expect your father and me to tidy up this mess.

Is the chaos intended? Maybe, rather than being a surreal fable, the film is a great meta-structural experiment whose narrative disorder mirrors its characters' adolescent turmoil.

Well, probably not. But it is very funny.