ABSTRACT
Acyclovir is a drug used to treat herpes virus infections including cold catch injuries, hot spots of genital organs, zona, AIDS, chicken pox and some other viral infections. The local cream of acyclovir is prepared in%5 packages, each gram containing 50mg of drug in a base of polyethylene glycol. Acyclovir cream [%5] in days 7, 8 and 9 of gestation was applied around their mouth [experimental group 1] and to the shared skin of other group [experimental group 2] twice a day in two hours intervals. Pregnant mice were sacrificed and dissected on day 15 of gestation and morphological and histological studies on the embryos and placenta were carried out. In the case of non-pregnant mice, the uteral born and ovaries were processed for histological investigations. Histological analyses showed significant decrease in embryogenesis and significant increase of abortion in experimental group 1 compared with control group. Significant increment was found in uterus diameter and thickness of endometrium when compared with control group. A pregnant woman should be very careful about applying acyclovir during the first trimester of pregnancy