Basic fibroblast growth factor (bFGF) is a strong mitogen for most mesoderm- and ectoderm-derived cells. Although bFGF exists in rat and human salivary glands, its physiological role in those glands is unknown. In this study, the effects of bFGF were investigated in monolayer culture of normal rat and human submandibular gland cells. Epithelial cells from rat and human submandibular glands were cultivated with the aid of 3T3 cells as a feeder layer. The effects of different concentrations of bFGF on the second passage of these cultured cells were examined. In both the rat and human cells, the percentage of bromodeoxyuridine (BrdU)-positive cells gradually increased up to 50 ng/ml, and then increased sharply at 100 ng/ml. However, at concentrations higher than 100 ng/ml, the percentages of BrdU-positive cells reached a plateau. In both rat and human cells, total cell numbers at 100 ng/ml bFGF were significantly higher than those of the control group from culture day 4. On the other hand, the morphology of the cultured cells showed no difference either with or without bFGF. These results indicate that a major effect of bFGF on salivary gland epithelial cells is to act as a mitogenic stimulus.