Background: Multiple dermatofibromas (DFs) are often associated with systemic lupus erythematosus (SLE). An increased number of mast cells is observed in the upper portion or over the lesion of DF Objective: To investigate the role of the serum of a patient with multiple DFs, we examined its growth effects on fibroblasts. Method: 3H-Thymidine incorporation was used to examine the effects of the serum of an SLE patient with multiple DFs on fibroblasts derived from DF and normal skin. Results: The serum of the SLE patient with multiple DFs exhibited a stronger growth-stimulatory activity on normal and DF-derived fibroblasts in a dose-dependent manner, compared to that of SLE without DFs or normal sera. The growth effects were inhibited in 40% by anti-platelet-derived-growth-factor antibody and almost completely inhibited by antibody against basic fibroblast growth factor. Cultured fibroblasts derived from the upper portion of the DF lesion, which included most of the numerous mast cells, demonstrated a higher level of 3H-thymidine uptake after stimulation of autologous serum compared to that from the mid and lower portions of DF. Conclusion: These results suggested the existence of various fibroblast growth factors derived from the mast cells in SLE patients with multiple DFs.