SUMMARY Plaice (Pleuronectes platessa) is a flatfish well-known for the ability to vary its body pattern, probably for camouflage. This study investigates the repertoire of patterns used by juvenile plaice, by describing how they respond to shifts between three artificial backgrounds. Two basic patterns are under active control, fine `spots' and coarser `blotches'. These patterns are superimposed on a fairly uniform ground. For the six plaice studied, the levels of expression of the spot and blotch patterns varied continuously and independently according to the visual background, and in a manner consistent with their being cryptic. The repertoire of plaice appears to be intermediate between the tropical flatfish Bothus ocellatus,which has three separate basic patterns, and two temperate species Paralichthys lethostigma and Pseudopleuronectes americanus,which have one each. It is interesting to consider how mixing a small number of coloration patterns is effective for camouflage, and why the demands of this task may lead to differences between species.