BACKGROUND: Patients with semantic dementia are impaired in both object naming and, to a lesser extent, in object use. To date there have been relatively few studies examining the relearning of object names, and only one examining the relearning of object use. No study has examined relearning object naming, definition, and use simultaneously. AIMS: To explore the relatedness of object naming, definition, and object use in semantic dementia; to explore whether or not therapy is effective; and to explore the effectiveness of errorless learning. METHODS and PROCEDURES: Two patients with mild to moderate semantic dementia and two matched control participants were tested in naming, defining, and demonstrating the use of 33 household objects. The quality of the definitions was rated as poor, adequate, or good by three independent raters. Three components of object use were examined: hold, orientation, and movement. The assessment was repeated with the patients following 3 weeks of therapy, and 1 month after completion of therapy. For the therapy, objects were divided into individual trained and untrained sets based on familiarity and performance at initial assessment. Patients received therapy sessions twice weekly, and engaged in independent practice. During the therapy sessions, the researcher modeled the name, definition, and use of each item, which the patient then repeated. In the independent practice each patient watched a DVD in which she named and defined the object and used it correctly. OUTCOMES and RESULTS: Patients were severely impaired on object naming and definition, but less so on object use. Both patients showed some improvement as a result of therapy, which was maintained at follow-up in one case. CONCLUSIONS: The results show that relearning in semantic dementia is possible. Factors affecting the results and the interaction between lexical and conceptual impairments are discussed. An unexpected finding of the study was that patients performed better in verb production both in the preliminary tests and in object definition.