A study investigated whether very young children use the concept of mutual exclusivity to make an initial link between a word and an object, and whether its use is linked to age or intelligence differences. Three groups of normally-developing children, aged 1 to 3 years, and three groups of older, mildly retarded children with similar levels of receptive language were asked to identify the object with an unfamiliar name, when presented with pictures of two objects. Results suggest that very young children do use the mutual exclusivity principle in making an initial link between a word and an object, at least with a small number of objects. However, young retarded children appear to have particular difficulty with the principle, suggesting that they may only be able to learn words presented in an exceptionally clear and unambiguous way. (MSE)