The effects of smooth muscle cells on the mechanical response of arterial walls were investigated for the common carotid arteries in culture. Tubular segments obtained from male Japanese White rabbits were cultured for 6 days in the unloaded state in DMEM+20% FBS. Prior to culture, half of the specimens were soaked in liquid nitrogen (liq-N2) for 20-40 seconds to kill cells in their walls. The mechanical response of the two groups following culture was examined using the pressure-diameter test and ruorphometry of the cultured segments. The arterial segments cultured without liq-N2 treatment had significantly smaller outer diameter than their uncultured counterparts over 80mmHg (P<0.02), and also their wall thickness was significantly reduced (P<0.005). These changes were not significant for the segments treated with liq-N2. These results suggest that mechanical response observed in the cultured arteries are attributable to active remodelling of arterial wall caused by smooth muscle cells.