Polypropylene slings are monofilament and multifilament meshes. Their features can impact clinical outcomes. We analyzed tissue reaction, inflammation, and the density of collagen fibers elicited by polypropylene meshes in the subcutaneous tissue of female rats. Thirty female Wistar rats underwent the implantation of 8x4-mm polypropylene meshes (two monofilamentar and two multifilamentar). The rats were killed at 7, 60, and 120 days after implant. Stereology was used to analyze the collagen fiber density. Acute inflammation was more intense in the early post-implant period (p=0.006), except for intravaginal slingplasty (p=0.342). Lymphoplasmocytic reaction was more intense in multifilament samples, even after 60 days (p<0.001) and 120 days (p=0.001). The stereological analysis showed significant differences between mono- and multifilament meshes, considering that monofilament meshes induced more collagen deposition and a greater density of collagen fibers (p<0.001). Multifilament meshes produced a more granulomatous reaction. The collagen fiber density was greater in monofilament meshes, which induced more favorable biocompatibility assessed objectively.191117-23