The embryotoxicity/teratogenicity of the sugar replacer isomalt was studied in Wistar rats and New Zealand White rabbits. Groups of 22-23 female rats were given diets containing isomalt at concentrations of 2.5, 5 or 10%, from day 0 to day 21 of pregnancy. The possible adverse effects of restricted feeding were studied in an additional group (food intake less than 80% of the control values). Groups of 36-37 female rabbits were given diets containing isomalt at concentrations of 2.5, 5 or 10%, from day 0 to day 29 of pregnancy. The female rats and rabbits were killed on days 21 and 29 of pregnancy, respectively. In both species no maternal toxicity occurred and no effects on reproductive performance nor on embryonic or foetal development were seen in any of the groups fed isomalt. The feeding of restricted amounts of stock diet to pregnant rats resulted in decreased maternal weight gain and lower uterus weights. Furthermore, this group had an increased number of resorptions and small foetuses, decreased foetus and placental weights and retarded bone development.