[Show abstract][Hide abstract]ABSTRACT: The aim of this study was to analyze the effects of synthetic para-nonylphenol isomers administered chronically throughout pregnancy and lactation on the reproductive system of mouse pups. The two synthetic isomers used in this study showed higher (3E22NP) or lower (44NP) estrogen receptor (ER) binding activity on in vitro yeast assay than a commercial NP (NPmix). Female mice were implanted with a tube filled with one of three NPs and estradiol-17 β (E2) before mating. The tube was kept in the mice throughout pregnancy and lactation period, until their pups had weaned at 28 days of age (PND 28). The data indicated that in males, NPs decreased body weight in some dose groups on PND28 and increased weights of testes and epididymides. However, the rate of seminiferous tubules having elongate spermatids (steps 10-16) decreased significantly in NPs and E2 treated groups, except for the 44NP groups. In female mice, NPs and E2 increased weights of ovaries, uterus and vagina in the pups in some dose groups on PND 28. However, there were no differences in the day of vaginal opening and numbers of corpus lutea. The present study demonstrates that the effects of these two isomers of NP on the pup reproduction at PND 28 are not quite different, despite them showing different levels of ER binding activity using in vitro yeast assay.