Pajama Men: Improv Show, Soho Theatre, London

For their latest show this sharp-witted and usually slumberwear-clad pair, who you'll normally never catch sleeping, have cast off crafted lines and practised clowning - and their normal stage attire - in favour of freeform improv in casual clothes.

The Pajama Men have perhaps spoilt us before, so this collection of medium form improv sketches was always going to be hard-pushed to compete. It's always a pleasure watching Shenoah Allen and Mark Chavez work, but tonight is really just a window on to their creative process, watching the means without a wholly satisfying ending.

Indeed, there's a sluggish pall over the first section where the duo grapple with basing sketches around the suggested word "Switzerland". Ideas morph into each other as the pair try and settle on a groove that feels right and is fruitful. It's amiable enough, with the high point watching Chavez miming getting dressed by 'catching' clothes that are thrown at him.

The pair cover themslves in a little more glory in a scene where two characters (called Oooh Oooh Oooh and Bob thanks to the audience's instinctive response to their request for names) write love letters to each other. "I drink ketchup when I am nervous" reveals Bob (Allen), utilising another audience suggestion for a random word.

Another sequence using just one word for its genesis (jumbo jet) generates lines more reminiscent of the two at their best. Disgruntled and murderous pilot Allen wonders: "Is A to B enough? Is B that great?" Chavez attempts to talk him down, promising him that one day their planes will go to C.

As ever the Americans value the journey, as much as the destination, but on this first night of this London run (that follows from a short Edinburgh run last month) it would be fair to say that they have some engine trouble along the way.

The erratic nature of the evening is rather underlined with the inclusion of a brief musical interlude care of Kevin Hume, a regular collaborator with the Pajamas, and a guest spot that is tonight filled by the scripted sketches of Late Night Gimp Fight. This quartet battle initial nonplussed indifference to warm an audience that has only intermittently been wowed tonight.

More of a mix of short, medium and long form improv might have been the way to structure this show. Fans of the Pajama Men might enjoy the behind-the-scenes feel of this as a lover of DVD box sets might enjoy extras. Newbies should be assured that the pair have much, much more to offer.