Myofibroblasts in pig granulating wounds have an identifiable life cycle that parallels the 8 wk span of contraction of the wounds. As seen by EM, fibroblasts with a contractile appearance became prominent within 1 wk after wounding and persisted for 12 wk after which time they were not visible. Large tangled filaments, measuring 120 .ANG. are prominent in fibroblasts in late contracted wounds and may be actin. Such filaments could preserve fibroblasts in a contracted state and allow time for the reorganization of collagen into a fixed rigid scar.