Recent grazing preference studies show that sheep offered a choice between large adjacent monocultures of perennial ryegrass and white clover choose a diet that is a mixture of the two species (ca. 0·7 white clover) (Parsons et al., 1994). One possible hypothesis to explain this is that animals need to sample different areas to know what is located there or the different plant species to know what eating each species represents and because of this include apparently less desirable foods (here ryegrass) in the diet (see Parsons et al., 1994). Edwards et al., (1996) showed that sheep can use spatial memory and so may not need to sample on an area basis. In this study, we tested directly whether sheep could distinguish between ryegrass and white clover without grazing them and whether they can form associations between the appearance of the vegetation and the food reward it represents.