Structures in which nouns modify nouns have raised questions about the form and functioning of generative grammars. By applying and extending Jackendoff's X-bar theory of phrase structure, the syntactic properties of two types of pre-noun modifiers, adjectives and nouns, can be examined. X-bar analysis correctly predicts many features of noun-noun modification structures. It appears that all of the salient properties of adjectives in the attributive position are shared by nouns in the pre-noun position, and that the predictions of the X-bar theory regarding the order of subcategorized modifiers and restrictive modifiers hold in noun-noun modification structures. (JL)