Four aphasic patients were tested in several tasks to determine their ability to use syntactic information. Two patients classified as Broca's aphasics and presenting markedly different levels of severity of aphasia were deficient in their ability to use syntactic information in sentence comprehension and construction. It is argued that the syndrome of Broca's aphasia undermines patients' ability to perform the syntactic analyses that are necessary to understand and to produce sentences in both language modalities. A third patient was a conduction aphasic who presented a pattern of sentence comprehension similar to the Broca patient, but produced no other evidence of syntactic impairment. The argument is advanced that the conduction patient's apparently selective impairment of syntactic processing in comprehension is actually a reflection of a severe auditory-verbal short-term memory deficit. The fourth patient was classified as a mildly-impaired Wernicke's aphasic, who presented no evidence of a selective disturbance of syntactic processing abilities. These results are interpreted as support for the hypothesis that the syndrome of Broca's aphasia results from an impairment to the syntactic component of the language processing system.