Enantioselectivity in the separation, toxicology, biodegradation and estrogenic activity of chiral pesticides has become a groundbreaking topic recently. In this study, real-time, quantitative polymerase chain reaction was adapted to investigate the induction of estrogen-responsive gene expression in embryo-larval zebrafish after 7 d of exposure to permethrin (PM) enantiomers. The PM enantiomers were completely separated by a chiral HPLC column. The in vivo study found that a 7 d exposure to 250 ng L(-1) PM racemate and its enantiomers was sufficient to stimulate vtg1, esralpha and cyp19b expression, while 1000 ng L(-1) exposure significantly induced gene expression in a pattern similar to that of the control (50 ng L(-1) E2), except for vtg2. Significant differences were detected between the enantiomers in the induction of estrogen-responsive gene expression. At the exposure level of 1000 ng L(-1), the vtg1, esralpha and cyp19b responses to the (-)-trans enantiomer were about 3.2-, 1.8- and 1.5-fold higher, respectively, than those in the group treated with (+)-trans enantiomer (p < 0.05). In the two cis-enantiomer treatment groups, (+)-cis increased the mRNA level of the cyp19b gene about 1.5-fold higher than the (-)-cis-enantiomer did. Of the four enantiomers, the (-)-trans enantiomer showed the greatest estrogenic activity. The results strongly indicate the occurrence of significant enantioselectivity in estrogenic activity of PM enantiomers exposed to embryo-larval zebrafish. These findings add to a growing body of evidence concerning enantioselectivity in the toxicity, endocrine-disrupting activity, and environmental biodegradation of chiral pesticides.