Fibroblast heterogeneity within normal tissues and the subsequent modulation in pathological settings are reflected by ultrastructural criteria and expression patterns of cytoskeletal proteins. The temporal or permanent expression of α‐smooth muscle (sm) actin in fibroblastic cells is generally related to the development of structural features typical of myofibroblasts. There is evidence of site specific subtypes of myofibroblasts and even of a histogenetic diversity. While granulation tissues myofibroblasts are derived from local fibroblasts, other cell types may also have the potential to acquire a myofibroblastic phenotype. Myofibroblast phenotype can be modulated by several agents such as cytokines (e.g., GM‐CSF and γ‐interferon) and extracellular matrix components.