Multiple-choice responses to incomplete sentence stems is a popular task for assessing and treating reading comprehension in patients with aphasia. This study investigated the influence of contextual constraint and response expectation on aphasic subjects' sentence-level reading comprehension. Constraint refers to the number of possible word completions available for a sentence stem. Expectation refers to whether the correct completions are expected or unexpected words. Subjects responded to stimulus items in which levels of constraint (high/low) and levels of expectation (expected/unexpected) were combined into four test conditions. Results indicated that the subjects performed worst on the low-constraint, unexpected-response sentences. They did significantly better with both increased constraint and with increased expectation. Both word pool and semantic feature activation are discussed as possible underlying mechanisms that influence aphasic subjects' reading comprehension of sentences.