A fusion polypeptide is described having the amino acid sequence X-Y-Z, or portion thereof, comprising the amino acid sequence of a glycosylated interferon-beta (X); Y is an optional linker moiety; and Z is a polypeptide comprising at least a portion of a polypeptide other than glycosylated interferon-beta. It is preferred that X is human interferon-beta-1a. Mutants of interferon-beta-1a are also described.