The present invention relates to process for reducing the endotoxin content of a sample of fermentation broth containing polysialic acid and endotoxin comprising the sequential steps: (i) adding to the sample a base having a pKa of at least 12 to form a basic solution having a pH of at least 12, incubating the solution for a pre - determined time at a pre - determined temperature; and (ii) recovery of PSA, suitably by (iii) passing the sample through an anion - exchange column whereby polysialic acid is absorbed on the ion exchange resin; (iv) washing the column with one washing buffer, whereby polysialic acid remains absorbed on the ion exchange resin; and (v) eluting the polysialic acid from the column using an elution buffer to provide a product solution of polysialic acid having reduced endoto xin content.
