Effortful, agrammatic speech and relatively intact comprehension often appear to coexist in Broca's aphasia. The present study focusses on this discrepancy, and tests the claim that the agrammatic patient has more information about syntactic structure than is indicated in his speech. Agrammatic aphasics and non-neurological patients sorted words from a variety of sentences on the basis of how closely related they felt the words to be in each of those sentences. These word groupings served as input matrices for a hierarchical clustering analysis. The resultant subjective phrase structure trees show that while normal subjects are often constrained by surface syntactic properties, agrammatic patients operate on a hierarchical scheme that excludes anything nonessential to the intrinsic meaning of a sentence. These findings suggest that expressive agrammatism is only one aspect of an impairment involving all language modalities.