Retroviral infection has been proposed as an etiologic factor in schizophrenia. In an effort to unmask a latent retrovirus, short term cultures of peripheral lymphocytes from 15 schizophrenic subjects and nine normal controls were exposed to ionizing radiation and co-cultured with indicator cells. Reverse transcriptase activity, a marker of retroviral infection, could not be detected in any of the cultures. Our findings are further evidence against a role for retroviral infection in the etiology of schizophrenia.