In recent years a cause-effect relationship between the existence of circulating antineuronal antibodies (CANA) and neurological paraneoplastic syndromes has been described by several authors suggesting specifity of such antibodies for paraneoplastic syndromes. The present study is a systematic approach to elucidate the significance of CANA in tumor patients. Forty patients with biopsy-proven small cell cancer of the lung (SCLC) were compared to 70 non-SCLC patients and 20 controls in respect to clinical and neurophysiological findings. CANA were found in 17 patients with SCLC. However, only one of these patients with SCLC and positive CANA displayed a sensory neuropathy of the Denny-Brown type, which appeared to be unrelated to CANA titers and oncological course. Contrary to recent reports, we were not able to confirm an association between the existence of CANA and an increased incidence of paraneoplastic neurological syndromes. These data suggest that the antineuronal antibodies appear to be specific for SCLC, but are not necessarily related to paraneoplastic neurological syndromes.