This subchronic study evaluated the potential toxicity of three viscosities of polydimethylsiloxane (PDMS) fluid. Nine groups of 20 male and 20 female Sprague- Dawley rats were fed 1, 5, or 10% PDMS fluid, with a viscosity of 35, 350, or 1000 cs, for 90 days in addition to the basal diet. Two additional groups of 20 male and 20 female Sprague-Dawley rats were fed only the basal diet and served as the controls. The diet was analyzed for homogeneity and stability at 1, 4, 8, and 12 weeks. Detailed ophthalmic examinations were conducted prior to study initiation and prior to terminal sacrifice. The animals were observed daily for mortality, changes in appearance or behavior, and signs of toxicity. The stools of the animals were examined visually for coating and consistency and the perianal region of the animals examined for evidence of anal leakage of the fluid. Body weights and food consumption were recorded weekly. Prior to terminal sacrifice, 10 animals/sex/group were selected for hematology and clinical chemistry evaluations and 5 of these 10 animals were used to collect urine for the urinalysis. After the 90 day feeding period, all remaining animals were sacrificed and selected organs were collected, weighed, and examined histopathologically. Bone marrow was also collected and analyzed. No changes in mortality, behavior, or appearance were observed. The incidence of anal leakage increased with percent fluid in the diet and decreased with increasing viscosity. The greatest incidence of leakage occurred in the 10%, 35 cs dose group. No changes in stool coating or consistency were observed. Food consumption and body weights were significantly increased in males, especially those in the 5 and 10% dose groups, for all viscosities. A few statistically significant differences in hematological and clinical chemistry parameters were reported. These included increased basophil count and chloride levels and decreased blood urea nitrogen. These changes did not persist nor did they occur in a dose-related manner, therefore they were not considered treatment-related. There were no significant differences in urinalysis data between control and treated animals. A few significant changes in organ weights, such as increased liver and kidney weights, were reported. These were also not considered to be related to PDMS administration. Corneal opacity, mild chronic corneal inflammation, and neovascularization were present in the eyes of treated animals. These ocular lesions were reported in treated animals in a non-dose related pattern and may have been due to direct ocular irritation from PDMS fluid in the feed. Three lymphomas were observed in treated rats, 2 in the 10%, 1000 cs group and 1 in the 1%, 35 cs group. These neoplasms were not confined to one organ system, nor was there a dose response, or an increased incidence compared to historical controls. Therefore these lesions were considered spontaneous and not treatment- related. Overall, the only treatment-related effects observed were the ocular changes attributed to direct contact of the PDMS fluid with the eyes of treated animals. No systemic effects were associated with the presence of PDMS fluid in the diet.