Macrophages are a source of many important mediators of wound repair. Cells of an established macrophage-like cell line (U-937) were exposed in vitro to one of two light sources with different levels of polarization (95% and 14%), The irradiation times of 60 and 120 s were such that the energy densities to which the cells were exposed were 1.44 and 2,88 J/cm² for each of the light sources, Other groups of cells were sham-irradiated as controls, Twelve h after exposure the macrophage-conditioned medium was removed and placed on 3T3 fibroblast monolayers. Fibroblast proliferation was assessed over a four-day period, The proliferative response was greatest in the cultures exposed to supernatants from macrophages treated with the 95% polarized light source. A treatment time of 120 s was more effective than that of 60 s.