IN this communication we report the presence of glycolyl-neuraminic acid in sialic acids from ox brain gangliosides. Our method of analysis consisted of the following six steps: (i) gangliosides were extracted from ox brain grey matter and purified according to a method which we have previously described1; (ii) gangliosides so obtained were hydrolysed in 0.1 N sulphuric acid at 80° C for 2 h, to split off sialic acid; (iii) sialic acid was purified on ‘Dowex’ 2 × 8 column as acetate according to Svennerholm2, and desalted on ‘Amberlite IR–120’; (iv) the solution was dried in vacuum and the residue was hydrolysed in 1 N sulphuric acid for 5 h at 100° C to obtain glycolic acid3; (v) glycolic acid was purified on ‘Dowex’ 2 × 8 column as acetate and eluted with NaCl 2 M; (vi) the glycolic acid was identified by the Eegriwe reaction4 and by gas-chromatography.