experimental evidence suggests that inorganic lead and benzo[a]pyrene ( bap ) suppress the development of primordial oocytes during fetal life . 
 we examined the single and combined effects of prenatal exposure to bap and moderate doses of lead . 
 the fertility and ovarian morphology of f1 female nmri mice in four treatment groups ( nine mice per group ) were investigated : control ; lead ( f0 given 1 g pbcl2/l in drinking water until mating ) ; bap ( 10 mg / kg body weight daily by oral intubation on days 7 - 16 of f0 pregnancy ) ; and combined lead and bap . 
 f1 groups exposed prenatally to bap either alone or in combination with inorganic lead showed markedly reduced fertility with few ovarian follicles compared to controls , whereas the group exposed to lead only had measures comparable to the controls . 
 mice exposed to both lead and bap had a significantly longer gestation period ( days to litter ) compared to mice exposed only to bap , lead , or controls . 
 there is a nonsignificant indication that the compounds together further reduce number of offspring , number of litters , and litter size . 
 these results suggest that lead and bap have synergistic effects on impairment of fertility . 
 the possibility of synergism may be of human relevance as inorganic lead and bap are ubiquitous environmental pollutants.imagesfigure 1.figure 2 .