BACKGROUND: Seronegative NMO is highly prevalent in non-Western countries implying the presence of as yet unknown antibodies (Ab). We investigated potential novel Ab in aquaporin-4 Ab (AQP-4-Ab) positive and negative NMO patients. METHODS: Sera of 20 NMO patients were examined for AQP-4, myelin oligodendrocyte glycoprotein (MOG) and glycine receptor (GlyR) Ab by cell-based assays. RESULTS: AQP-4-Ab was identified in 10 NMO patients, MOG-Ab was detected only in one AQP-4-Ab positive patient and GlyR-Ab was detected in two AQP-4-Ab negative patients. GlyR-Ab positive patients displayed simultaneous optic neuritis and transverse myelitis attacks and relatively low disability, whereas MOG and AQP-4-Ab double positive patient had a significantly increased disability. CONCLUSION: This study showed for the first time the presence of GlyR-Ab in Turkish NMO patients. In contrast with previous reports, MOG Ab does not appear to be a distinctive marker for Turkish AQP-4-Ab negative NMO patients.