This paper presents a series of therapy studies aimed at remediation of the word-retrieval deficits of three aphasic patients. All three patients are argued to have semantic deficits and are given semantic therapy in the form of word-to-picture matching tasks. Two of the patients show improved naming as a result of the therapy, with generalization to untreated items. The 3rd patient does not improve as a result of the word-to-picture matching therapy, even though her pattern of deficits appears similar. However, she does show item-specific improvement in naming with a different therapy (lexical therapy). The reasons for the differences between the patients in their response to therapy are discussed. In particular the effect of the production of the word during the therapy is considered, and the patient's ability to perform the task accurately. Additionally, we investigate the role of modality of input and generalization across modality of output, and the use of different types of semantic therapy. The study highlights the importance of analysing tasks in detail, and the need to continuously evaluate the effects of intervention.