PEG-urate oxidase and its use.

A conjugate of uricase that retains at least about 75% of the uricolytic activity of unconjugated uricase and is substantially non-immunogenic, and comprising a purified uricase comprising subunits in which each subunit of said uricase is covalently linked to on average, between 2 and 10 strands of PEG, wherein each molecule of PEG has a molecular weight between 10 kDa and 100 kDa.