Mice were injected intraperitoneally with either amosite, crocidolite or chrysotile. Tissue specimens of the mesentery (appendices epiploicae) were taken after 2 h, 24 h and 7 days and prepared for scanning electron microscopy. Subsequent examination revealed numerous fibers penetrating the mesothelium. The penetration is regarded as the earliest interaction between fibers and mesothelium and is due to the asbestos' inherent needle-like structure and to visceral motility.