The embryotoxicity/teratogenicity of neohesperidin dihydrochalcone (NHDC) was examined in Wistar Crl:(WI)WU BR rats. NHDC was fed at dietary concentrations of 0, 1.25, 2.5 or 5 to groups of 28 mated female rats from day 0 to 21 of gestation. At Cesarean section 25, 22, 23, and 23 rats were found to be pregnant in the control, low-, mid-, and high-dose group, respectively. The NHDC treatment was well tolerated and all animals survived till the end of the study. Body weights (bw) and body weight gains did not differ between controls and NHDC treatment groups. The intake of NHDC was 0.8-0.9, 1.6-1.7, and 3.1-3.4g/kg bw/day for the low-, mid-, and high-dose group, respectively. Except for cecal enlargement, there were no changes observed at necropsy which could be related to the NHDC treatment. All dams had viable fetuses. The fecundity and gestation index, the number of corpora lutea, implantation sites, live and dead fetuses, early and late resorptions, pre- and post-implantation losses, and sex-ratio were not affected by the treatment. There were no differences for the mean weight of the gravid and empty uterus, ovaries, and placenta between the NHDC treatment groups and the controls. Examination of the fetuses for external, visceral, and skeletal changes did not reveal any fetotoxic, embryotoxic or teratogenic effects of NHDC. In conclusion, no adverse effects were observed at NHDC levels of up to 5% of the diet, the highest dose level tested, at which the rats consumed about 3.3g/kg body weight/day. The observed cecal enlargement is a well-known physiological, adaptive response to the ingestion of high doses of a low-digestible substance and is generally accepted to lack toxicological relevance. © 2004 Elsevier Inc. All rights reserved.