The purpose of this study is to search for cues that could account for the fact that right-hemisphere lesions affect word naming when the criterion for naming is semantic. The authors analyzed the errors as well as the time course of productions of 35 vascular right-brain-damaged subjects (RBD) and 20 control subjects (C) in a semantic-based word-naming task. Results show that there are no differences between groups in terms of (a) the number of errors produced and, (b) the patterns of error types. However, results also show a reduction of verbal fluency for semantic criteria in RBD-subjects present only after the first 30 seconds of production. These results indicate that reduction of word production in RBD-subjects is not the consequence of nonspecific factors such as perseveration or spontaneity, but reflects problems with the less automatized processes permitting exploration of semantic organization, either because scanning process are affected, or because the presence of a discreet semantic impairment prevents scanning from being as efficient. Given that efficient exploration of semantic knowledge is important for lexico-semantic functioning, the present results suggest that the right hemisphere contributes to some aspects of lexico-semantic processing necessary for language production.