We report for the first time Na and O abundances from high-resolution , high S / N echelle spectra of 20 red giants in NGC 2808 , taken as part of the Science Verification program of the FLAMES multi-object spectrograph at the ESO VLT . In these stars , spanning about 3 mag from the red giant branch ( RGB ) tip , large variations are detected in the abundances of oxygen and sodium , anticorrelated with each other ; this is a well known evidence of proton-capture reactions at high temperatures in the ON and NeNa cycles . One star appears super O-poor ; if the extension of the Na-O anticorrelation is confirmed , NGC 2808 might reach O depletion levels as large as those of M 13 . This result confirms our previous findings based on lower resolution spectra ( Carretta et al . 2003 ) of a large star-to-star scatter in proton capture elements at all positions along the RGB in NGC 2808 , with no significant evolutionary contribution . Finally , the average metallicity for NGC 2808 is [ Fe/H ] = -1.14 \pm 0.01 dex ( rms = 0.06 ) from 19 stars .