Advanced glycation end products of bovine serum albumin (AGEs-BSA) exhibited biphasic effects on the proliferation of cultured rabbit vascular smooth muscle cells (VSMCs) in terms of [3H]thymidine incorporation and cell number count; a stimulatory effect was observed at 1-10 micrograms/ml and an inhibitory effect at more than 20 micrograms/ml, while it inhibited [3H]thymidine incorporation even at 1-10 micrograms/ml in cultured bovine vascular endothelial cells (VECs). Transient activation of p42 mitogen-activated protein kinase (MAPK) with a peak at around 5 min and a subsequent sustained phase was induced by AGEs-BSA in VSMCs, but not in VECs. The dependence of MAPK activation on AGEs-BSA dose was correlated with that of VSMCs proliferation.