Prior experiments have shown that the functioning of hamster oviducts is impaired by in vitro exposure to cigarette smoke. To determine if cigarette smoke affects oviductal functioning in vivo, an inhalation experiment was done in which hamsters were exposed to doses of smoke similar to those received by human smokers. The effects of mainstream smoke (the bolus of smoke inhaled by active smokers) and sidestream smoke (the main component in environmental tobacco smoke) were compared. Transport of preimplantation embryos through the hamster oviduct was retarded in females inhaling doses of mainstream or sidestream smoke that produced serum cotinine levels within the range reported for women who actively or passively smoke during pregnancy. In addition, hamster oviductal muscle contraction rate decreased significantly during a single exposure of animals to either mainstream or sidestream smoke, and contraction rate failed to return to initial control values during a 25-min recovery period. Both preimplantation embryo transport and muscle contraction were more sensitive to sidestream than mainstream smoke. These data demonstrate that inhalation of doses of mainstream and sidestream cigarette similar to those received by active and passive human smokers adversely affects functioning of the oviduct and may explain the increased incidence of ectopic pregnancies reported in women who smoke.