The effect of culture conditions on calf dorsal aorta endothelial cells was studied. Population doubling time varied as a function of the cell seeding density, growth Medium, serum supplement, and concentration of fibroblast growth factor (FGF). The shortest population doubling time was found for cells (population doubling level 0--30) grown in Eagle's Minimal Essential medium (MEM) supplemented with 10% fetal bovine serum (FBS) and 100 ng/ml FGF. The stimulatory effect of FGF on bovine endothelial cell proliferation was dependent on cell inoculation density. FGF significantly increased cell division rate at cell inocula less than 1 x 10(4) cells/cm2 but not at higher densities. The population doubling time and cell size increased as the mass culture population doubling level increased. The replicative lifespans of bovine endothelial cells grown in medium supplemented with 20% FBS were 10--15% greater than parallel cultures supplemented with 10% FBS. Cultures grown in medium supplemented with 10% FBS and 50 ng/ml FGF showed a 50% increase in replicative lifespan compared to cultures grown in medium supplemented with 10% FBS alone. When FGF was used the increase in the number of doublings was a function of the length of time the cells were grown in the presence of FGF. This report extends comparable observations on the in vitro aging of human diploid fibroblasts to bovine endothelial cells.