Our privious study proved that there were high affinity HDL_3—binding sites (HDL receptor) on the membrane of human SMMC—7721 hepatoeareinoma cells and the bindings of FITC-labelled Apo E—free HDL_3 (FITC—HDL_3) and native HDL_3 to the cells were competitive. This paper showed that modification of HDL_3 by aeetyl imidazol decreased its competitive binding to the cells. This inhibition was dose—dependent with the maximum inhibition at 1 mol/L of aeetyl imidazol. Our results suggest that tyrosin residue in HDL is present in the HDL binding recognition site and takes part in the binding to its receptor.