The distribution of glass fibers in the peritoneal cavity of the rat was investigated at 2, 24, and 48 h following intraperitoneal injection of 7 mg of material using a radioactive tracer technique. At each time point the peritoneal cavities of the rats killed were lavaged with 20 ml of physiological saline to recover fibers not yet attached to tissue surfaces. At 2 h, 35% of the administered fiber could be recovered by lavage, but at 48 h this was reduced to 2%. At 48 h, the amount of fiber associated with the abdominal organs and the abdominal wall was roughly in proportion to their surface areas. The weight of fiber associated with the various tissues was in the following order: gastrointestinal tract > liver > carcass (abdominal wall) > diaphragm > urogenital tract > spleen > kidneys.