Siloxanes and silicones, di- me, hydroxyl stopped (CAS No. 70131-67-8) was evaluated in a chronic dietary study. One group of 5 male and 5 female albino FDRL rats was fed 0.05% polydimethylsiloxane hydroxy-functional fluid in addition to the basal diet for 12 months. An additional group of 10 male and 10 female albino FDRL rats was fed only the basal diet and served as controls. The animals were observed daily for appearance, behavior, general physical condition, and survival. Body weights and food consumption were recorded weekly for the first 12 weeks. Body weights were recorded biweekly thereafter. Hematological evaluations and urinalysis were conducted after 3, 6, and 12 months and clinical chemistry parameters were examined after 12 months. At the end of the 12 month feeding period, the animals were sacrificed and necropsied. Organ to body weight ratios were calculated and selected tissues were examined histopathologically. No differences in behavior, general appearance, food consumption, or survival were reported. The treated males gained significantly more weight than control males during the study period. No treatment-related effects on hematological or clinical chemistry parameters or urinalysis were reported. No significant alterations in the absoluteor relative organ weights or changes in gross pathology or histopathology were reported.