Acidic (a) and basic (b) fibroblast growth factors (FGFs) are two related mitogenic and angiogenic factors. They are multifunctional in that they can affect proliferation and induce or delay differentiation. Both aFGF and bFGF were shown to stimulate proliferation of calvaria cells in situ as well as osteoblast-enriched calvaria-derived cells. bFGF was also found to suppress the expression of alkaline phosphatase, parathyroid hormone stimulatable adenylate cyclase, osteocalcin, and type I collagen in the osteoblastic ROS 17/2.8 cells. To explore a possible role for guanine nucleotide binding proteins we assessed the effects of pertussis toxin (PT) on FGF action. PT had opposite effects to those of bFGF on all parameters examined.