Mechanisms of lexical retrieval within natural semantic categories are investigated in patients with schizophrenia. We predicted and found that schizophrenics show lexical retrieval impairments on word search tasks. Experiments are described in which subjects either scan through word lists for single target items (simple search), or search for members of a semantic category (semantic search). Two groups of subjects are employed: medicated schizophrenics, and a comparison group with similar age and premorbid intelligence. A significant between-group difference is reported (for both speed and accuracy) in semantic category search but not in simple search. It is known that many schizophrenic patients have word finding difficulties (Frith, 1992; Frith et al., 1991). Our results support the claim that in some schizophrenics at least, selective lexical-semantic parallel processing deficits may underlie word finding aberrations. It is possible that such dysfunctions reflect weakened connection strengths between units making up a lexical-semantic field (as characterised by proximity to a prototype).