Recent research has provided evidence that certain psychophysiological dysfunctions are present in non-psychotic biological relatives of schizophrenia patients. A new candidate for such studies is the visual backward masking (VBM) dysfunction. In this study, the authors compared the VBM and Wisconsin Card Sorting Test (WCST) performances of unaffected siblings of schizophrenia patients with that of normal volunteers with a negative family history. In the BM test, a briefly presented target letter must be recognized, which is followed by an irrelevant stimulus (mask). The WCST assesses higher-level cognitive (prefrontal) functions of categorization and attentional set-shifting. Despite their intact psychosocial and general intellectual functions, the unaffected relatives of schizophrenia patients showed lower BM performances in comparison with the controls, which was restricted to short interstimulus intervals (< 60 ms). In the controls, there was a non-linear (N-shaped) masking function, whereas in the relatives no similar effects were found. There was no significant difference in the WCST performances. These results suggest that the dysfunction of early sensory-perceptual processes is a trait marker of schizophrenia.