I report a series of single case studies involving an aphasic patient, H.G., which illustrates both the usefulness and the limitations of cognitive neuropsychological models and methods in aphasia rehabilitation. The first set of experiments analyze H.G.'s pattern of performance across lexical tasks in order to identify the loci of her damage to the cognitive mechanisms underlying the tasks of naming, comprehension, repetition, reading, and spelling. The second set of studies evaluates her response to two different types of treatment and identifies a few of the variables that influence the effectiveness of treatment. (JINS, 1998, 4, 648–660.)