AbstractChlorophyllin (CHL) has proven that there is antimutagenic and anticarcinogenic activity in several organisms without causing lethal effects. However, there is no information about its effects when it is administered in gestation. In the present study, we assessed possible effects of CHL when it was administered to CD‐1 mice on the 8th day of gestation using the same doses and administration route used in ours previous antimutagenic and antigenotoxic studies. Females were exposed to a single dose of CHL by i.p. injection (20, 40, 50, or 100mg/kg b.w.). On day 18 all dams were subjected to cesarean section and the fetuses were examined with common teratological methods. Results show that CHL‐treatment induced total litter loss and is dose‐dependent, probably due to either the interaction between CHL and some general control mechanisms of embryo development or by an impairment of maternal‐fetal interactions. The analysis of uterine horns of the CHL‐treated females with total litter loss revealed the presence of green rings in the uterus. Results show the inverse relationship between the number of live implants and the frequency of green rings, indicating implantation sites where embryo death and early resorptions occurred. Although CHL was given in a single dose on day 8 in this study, the results indicate that CHL is associated with significant embryo lethality. Teratogenesis Carcinog. Mutagen. 22:461–471, 2002. © 2002 Wiley‐Liss, Inc.