Objective and Methods: We investigated the effects of several growth factors on [3H]thymidine incorporation and procollagen type I carboxyterminal propeptide (P1CP) production, which reflects type I collagen metabolism, in keloid and normal fibroblasts. Results: Six fibroblast cell strains, derived from keloid or normal skin, exhibited similar growth responses to platelet-derived growth factor, transforming growth factor β1 (TGF-β1), γ-interferon (γ-IFN) and histamine. In contrast, keloid fibroblasts showed significantly greater growth response to epidermal growth factor (EGF) than normal fibroblasts. PICP production was 4.4 times higher in 6 strains of keloid fibroblasts than in 6 controls. Treatment with γ-IFN (100 U/ml) decreased P1CP production in both groups; the effect was significantly greater in keloid fibroblasts. TGF-β1 treatment upregulated PICP production in both groups. Treatment with histamine increased P1CP production in keloid fibroblasts, although it did not change that in the controls. Conclusion: EGF and histamine may play some role in the development of ke