to examine the toxicity of cyclosiloxanes ( css ) , the predominant low molecular weight cyclic silicones found in breast implants , we injected female cd-1 mice intraperitoneally with different doses of distillate ( 3.5 - 35 g / kg body weight ) containing cyclosiloxane d3 ( hexamethylcyclotrisiloxane ; cs - d3 ) , cyclosiloxane d4 ( octamethylcyclotetrasiloxane ; cs - d4 ) , cyclosiloxane d5 ( decamethylcyclopentasiloxane ; cs - d5 ) , and cyclosiloxane d6 ( dodecamethylcyclohexasiloxane ; cs - d6 ) . 
 the distillate was found to be lethal and all the mice injected with 35 g / kg died within 5 - 8 days . 
 the median lethal dose ( ld50 ) for distillate was estimated to be approximately 28 g / kg . these mice developed inflammatory lesions of the lung and liver as well as liver cell necrosis with elevated serum levels of alanine aminotransferase , aspartate aminotransferase , and lactic acid dehydrogenase . 
 administration of cs - d4 alone also produced lethality in these mice with an ld50 of 6 - 7 g / kg . 
 cs - d4-treated mice also exhibited pulmonary and hepatic lesions and elevated serum enzymes . 
 analysis of ld50 data indicates that cs - d4 is about as toxic as carbon tetrachloride or trichloroethylene . 
 we measured hydroxyl radical formation in cs - d4-treated mice and found increases of approximately 20-fold in liver and approximately 7-fold in lung on day 4 following injection . 
 our findings are significant because in vitro experiments have demonstrated that css can migrate out of breast implants , and in mouse experiments css have been shown to be widely distributed in many organs after a single subcutaneous injection and to persist for at least a year.imagesfigure 1figure 2figure 3figure 4