Aim: To investigate the distribution change of low density lipoprotein (LDL) receptors on the surface of EC effected by PACAP for understanding the potential mechanism of PACAP in atherosclerosis.Methods: EC were cultured with M199 containing 10-8 mol/L PACAP(PACAP groups) and M199 (control groups) respectively for 24 h, then incubated with 0. 5% BSA-M199-colloidal gold LDL conjugate solution for 2 h at 4℃. In addition, some of EC were warmed to 37℃ for 2 h to initiate endocytosis. Sections of 60 nm thickness were cut and observed with a HITACHIH-600 transmission electron microscope.Results: Colloidal gold LDL conjugate in control group often appeared in cluster, randomly distributed on the surface of EC and the percentage of clustering appearance was 65%. Effected by PACAP for 24 h,the percentage of single colloidal gold LDL conjugate increase to 50%, compared with control groups (P<0. 05). Warmed to 37℃ for 2 h, the EC of PACAP groups could decrease endocytosis of colloidal gold LDL conjugate.Conclusion: After PACAP treatment, compared with the control group, the percentage of single colloidal gold LDL conjugate granule appear in each cluster of EC seems to be increased and the endocytosis of colloidal gold LDL conjugate granules decreased.The change of distribution of singIe colloidal gold LDL conjugate granule represent less LDL receptors located on the surface of EC and can decrease transportation of LDL though EC when clusters are not formed.Thus, our results suggest that PACAP play an important role in the function of antiatherosclerosis.