Dimethyltin dichloríde (DMDC) is commonly used as a stabilizer in PVC pipe used for transport of potable water. Learning deficiencies have been observed postnatally in pups from DMDC‐treated dams. Studies were conducted with female Sprague‐Dawley rats to determine whether DMDC was absorbed by the dam and transferred across the placenta to fetal blood and brain tissue. This was accomplished in three phases: (1) a comparison of absorption of organic and inorganic tin from drinking water, (2) a comparison of prenatal and postnatal levels of tin in the pups in cross‐fostering studies, and (3) a [14C]dimethyltin dichloríde tracer study to determine whether organic tin passed to the pup intact Major findings include: (1) DMDC is absorbed in the gastrointestinal tract of the dam much more rapidly than Sn2+; (2) the more rapid absorption of DMDC results in higher concentration of tin in fetal blood and brain; and (3) in fetuses that receive tin as DMDC, both tin and the methyl carbon are absorbed by the dam and transferred to the blood and brain of the fetuses.