Airway smooth muscle proliferation is a key component of airway wall remodelling that occurs as a consequence of inflammation in asthma. Studies were conducted to examine the effect of dexamethasone on airway smooth muscle cell (ASMC) proliferation in vitro. Dexamethasone (25-250 nM) significantly inhibited DNA synthesis and cell division induced by beta-hexosaminidase A (Hex A, 50 nM) in bovine ASMC. The inhibitory effect of dexamethasone on DNA synthesis was variable depending on the growth factors: significant effect was observed on Hex A and insulin; no significant effect was observed on epidermal growth factor and fetal bovine serum.