A guinea pig partial thickness skin excision model was used to evaluate the effects of recombinant human PDGF-BB, PDGF-AA, EGF, and bFGF on granulation tissue (neodermis) formation. These growth factors tended to increase the thickness of the granulation tissue bed when assessed histologically at day 7. Using only four animals per group, PDGF-BB at 30 and 100 mug/ml consistently and significantly increased the thickness of the granulation bed 2-3 times that of control. Except for the increased thickness, the granulation tissue appeared normal. PDGF-AA and EGF also significantly increased the granulation tissue thickness, and bFGF gave indications of an effect. There was no evidence of synergistic effects between PDGF-BB, EGF, and/or bFGF.