The Piers-Harris Self-Concept Scale and the Coopersmith Self-Esteem Inventory were administered orally to 46 mentally retarded adults employed in a sheltered workshop. In-depth analysis of transcripts of the taped testing sessions revealed that the majority of the item responses were ambiguous and not readily scorable within the standardized procedures. Characterization of the problematic response patterns indicated assorted qualifications, contradictory assertions, and responses which had little relevance to the item content. Of those factors that might account for these ambiguous responses, it appears that social desirability, acquiescence, personal agendas, recipient design errors, and lack of item comprehension are among the most salient.