Female pregnant mice were fed chrysotile asbestos suspension by gavage to determine whether there is transfer of fibers to the fetuses. Groups of mice were given 2 doses of either 50 microg chrysotile suspension in 0.2 ml sterile normal saline (treated), or 0.2 ml saline (control), and were allowed to mate 2 d later. After pregnancy was confirmed, the treated and control groups received 2 additional doses of chrysotile asbestos or saline on gestational d 7 and 12. Both groups were allowed to deliver naturally, and the pups were sacrificed at 8, 1, 19, or 20 d after birth. The lungs and liver of two pups from each mother were processed for fiber counts using electron microscopy and energy-dispersive x-ray analysis (EDXA). All pups of the treated group had chrysotile fibers, while none were present in pups from controls. The mean fiber count of the lungs of treated group of pups was 780 fibers/g, and the mean fiber count of the liver was 214 fibers/g. Mean length of the fibers in the lung and liver was 18.48 microm and 18.30 microm, respectively. The fibers were thin, measuring 0.42 microm and 0.33 microm in the lung and liver, respectively. There was no significant difference in the weight gain between the treated and control group of pups. The postnatal fetal mortality of the 2 groups, 8.2% for the treated and 4.5% for the control group, were not statistically significant. To our knowledge, this is the first animal study to demonstrate that oral ingestion of chrysotile asbestos during pregnancy results in transfer of asbestos fibers to the fetuses.