We exposed Xenopus tropicalis to 1, 3.3, 11 and 36 ug/L octylphenol from Neiuwkoop-Faber (NF) state 46 tadpoles through adulthood in a flow-through water system. At NF stage 5, a random subsample of froglets was collected and assessed, while the remaining frogs were exposed through 31 weeks. Significant induction of vitellogenin was observed in the high treatment at the larval subsampling for both sexes, but not at the final sampling for either sex. No significant deviation from control for sex ratio was observed for either sampling period, suggesting minimal to no effect on gonad differentiation. Oviduct development was observed in males exposed to octylphenol. These results indicate that octylphenol exposure can induce vitellogenin in immature froglets and the development of oviducts in male adult frogs. The lack of effect observed on the developing gonads suggests that in amphibians, secondary sex characteristics are more susceptible to estrogenic compounds than developing gonads.