Abstract5‐bromo‐6‐methoxy‐5,6‐dihydro‐3′‐azidothymidine‐5′‐(p‐bromophenyl) methoxyalaninyl phosphate (WHI‐07), a novel bromo‐methoxy‐substituted aryl phosphate derivative of zidovudine (ZDV), is a potent dual‐function contraceptive agent with anti‐HIV activity. Its potential for reproductive toxicity was assessed in a series of experiments using CD‐1 mice under the conditions of its intended use as an intravaginal microbicide. Female CD‐1 mice were exposed intravaginally to a gel–microemulsion formulation containing 0%, 0.5%, 1.0% or 2.0% WHI‐07 for up to 13 weeks. On a molar basis, these concentrations represent 1400–5700 times its in vitro spermicidal IC50 and 1.4–5.7(×106) times its in vitro anti‐HIV IC50. We examined the effects of intravaginally administered WHI‐07 on: ovulation efficiency; in vivo fertilization and early embryonic, fetal development; and reproductive outcome, including neonatal survival and pup development. Compound WHI‐07 was administered intravaginally during superovulation, organogenesis and prior to mating for 5 and 10 consecutive days and for 13 weeks, respectively. Mice were evaluated for ovulation efficiency and fertilization rate and cleavage 14 and 40 h after human chorionic gonadotropin (hCG) injection, respectively. Pregnant mice were administered 2% WHI‐07 intravaginally during gestation days (GD) 6–15 and measures of teratogenicity were evaluated on GD 17. For short‐term toxicity study, mice were given intravaginal treatment of gel–microemulsion containing 0%, 0.5%, 1.0% and 2.0% WHI‐07 for 13 weeks and then mated with untreated males to evaluate potential reproductive and developmental effects. Repeated intravaginal exposure of mice to 2% WHI‐07 had no adverse effects on ovulation response, mean number of eggs recovered or the percentage of eggs fertilized or cleaved. No evidence of reproductive toxicity, fetal toxicity or teratogenicity was found following repetitive intravaginal application of 2% WHI‐07 during the period of organogenesis. Furthermore, repeated intravaginal exposure of mice to 0.5–2.0% WHI‐07 for 13 weeks had no adverse effect on the subsequent reproductive capability, perinatal outcome or growth and development of the offspring. Compound WHI‐07 shows unique clinical potential as a safe, dual‐function vaginal contraceptive for curbing mucosal and perinatal HIV transmission. Copyright © 2001 John Wiley & Sons, Ltd.