The scavenging effect of 2,6-diisopropylphenol on hydroxy radicals produced by xanthine oxidase was assessed by evaluating the in vitro depolymerisation of hyaluronan in artificial synovial fluid by size-exclusion chromatography. After 1 hour, the number-average molecular weight of hyaluronan remained unchanged (100%) with 2,6-diisopropylphenol, whereas it dropped to 90% with methylprednisolone added, to 55% with the antioxidant 2,6-tert-butyl-4-methylphenol added, and to 10% of its initial value in the absence of scavenger.