The absorption, distribution, metabolism and elimination of octamethylcyclotetrasiloxane were investigated in 2 monkeys administeredsingle oral doses at a level of 50 mg/kg. The C14-labeled test article was distributed throughout the body and it was absorbed mainly from the gastrointestinal tract. Residual 14C tissue levels 240 hours after oral dosing in microgram/gm equiv. were the following; 3.6 in lymph node, 8.4in mesentery, 13.1 in fat and 5.3 in liver. The major portion of radioactivity excreted was found in the urine with total recoveries of C14 at 63% and 52% while fecal recoveries were 11% and 16% of C14. Threemetabolites were observed; dimethylsilanediol, tetramethyl-1,3-disiloxane diol and hexamethyl-1,5-trisiloxane diol. Themetabolism closely paralled that of 2,6-cis and 2,6-trans-diphenylhexame thylcyclotetrasiloxane.