The present invention provides compositions and methods for modulating the expression of Hyaluronan (HA). In particular, this invention relates to compounds, which hybridize with nucleic acid molecules encoding hyaluronan synthase (HAS), particularly HAS isoforms HAS1, HAS2 and HAS3. These compounds may range in size from oligonucleotides to full length sequences. Such compounds are exemplified to modulate proliferation, such as cancer and inflammatory disorders, such as arthritis. It will be understood, however, that the compounds can be used for any other condition in which HA is involved.