This study evaluated hepatic changes in rats administered dimethylcyclosiloxane fluid. Two groups of male CD rats (10 per group) were administered 0 or 1600 mg dimethylcyclosiloxane fluid/kg/day by gavage for 14 days. Two additional groups received the same treatment but were examined using a DNA assay not discussed here. The animals were observed for mortality, other signs of toxicity, and changes in food consumption. In addition, the animals were weighed prior to study initiation, on day 7, and prior to terminal sacrifice. After the treatment period all surviving animals were sacrificed and the livers weighed, fixed using perfusion fixation, and prepared for examination via light and electron microscopy. Morphometric examination of the livers included determination of the total number of cells per liver, number of cells per volume of liver, and the average diameter of cell profiles in each lobular zone. No changes in body weight or food consumption, no deaths, and no signs of toxicity were observed. No difference in the number of cells per volume of liver was reported. However, the was a significant increase in the number of hepatocytes and in the total volumes of the livers of the treated group. In addition, liver weights of the treated animals were significantly increased relative to controls. No significant differences in mean hepatocyte diameter were observed, indicating hepatocellular hypertrophy was not present. These findings suggest that hyperplasia was the cause of hepatomegaly in rats exposed to dimethylcyclosiloxane fluid.