The regulation of endothelial cell (EC) and smooth muscle cell (SMC) proliferation following vascular interventions is critical to clinical efficacy. Our laboratory has developed a method of impregnating biomaterials with suspensions containing bioactive proteins resulting in the capability of differentially modulating EC and SMC growth in vitro and in vivo following implantation. We have previously reported that 60 mu internodal distance ePTFE grafts impregnated with fibrin glue (FG) containing FGF-1 and heparin develop confluent endothelialization with transiently increased EC and SMC proliferation after 4 weeks in dogs. Thoraco-abdominal implants after 20 weeks were developed significantly thicker (139 mu) inner capsules in response to the FGF. To minimize SMC proliferation we studied the effects of FGF-1, heparin, and thrombin concentrations on SMC growth in vitro. FG caused a 182% increase (P < 0.001) in DNA synthesis. Heparin within FG diminished this effect in a dose-dependant manner, with complete inhibition of FG-induced growth at 500 U ml-1 (versus FG alone, P < 0.001). FGF-1 within FG without heparin had no effect, but together, FGF-1 caused a dose-dependant growth increase while increasing heparin concentrations initially increased and then decreased proliferation. FGF-1 and heparin in the medium of quiescent SMCs had similar effects. Only thrombin concentrations > 3.2 U ml-1 stimulated SMC growth and this stimulation was blocked by heparin. A synergism between FGF and heparin on EC proliferation was also found but without EC growth inhibition in response to higher concentrations of heparin. It is thus possible to modulate the relative proliferative activity of ECs versus SMCs by altering the FGF:heparin ratio. This same system may be useful with other proteins to induce other local affects by the applied protein or systemic affects following release of that protein.