In rats of the present (re-derived) Wistar-Porton strain that are dosed either intravenously (i.v.), or intraperitoneally (i.p.) with Cd (1.25 mg/kg body weight) on day 12 of gestation (gd 12), foetal uptake of Cd is at least 6-fold greater than that reported in an earlier study (Webb and Samarawickrama 1981). Higher doses (1.5 and 2.0 mg/kg body weight) are lethal to the maternal animal when administered i.v., but not if given ip. The foetotoxicity of i.p. injected Cd, however, increases with the dose over the range 1.25-2.0 mg Cd/kg body weight. The teratogenic response, which is also wider than that observed previously, is maximal after the injection of 1.25 mg Cd/kg body weight i.v. on gd 10 and i.p. on gd 12. Whilst the incidences of hydrocephalus, urogenital abnormalities, cleft palate and other less common defects are similar after dosing by both routes, the incidence, range and severity of skeletal malformations are greater after i.p. than after i.v. administration of Cd on gd 12. This difference in response is unlikely to be explained by a difference in either foetal, or placental uptake of the metallic ion since, at 4 h after i.p. dosing, the foetal concentration of Cd is not significantly different from that after i.v. injection, whilst the placental concentration is about 33% less. It is suggested that damage to the maternal liver, which is more severe after the i.v. injection of the optimum dose, may be an additional factor that, in conjunction with the inhibition of transport in the placenta and biosynthetic processes in the embryo/foetus, contributes to the teratogenic effects of Cd in the pregnant rat.