Ovariectomized and immature frogs were injected with estradiol, testosterone, dihydrotestosterone (DHT), or a combination of estradiol with one of the androgens. Controls were treated with oil. Dry oviduct weights were compared across groups. Ovariectomized animals treated with testosterone or estradiol plus testosterone had the largest oviducts, whereas oviducts were slightly smaller in groups treated with estradiol alone. DHT had no effect in mature ovariectomized animals and only a very slight effect in immature animals. Protein content of oviducts showed little significant difference between groups. These results suggest that oviduct growth in testosterone-treated animals may be due to aromatization of testosterone to estradiol. To test this hypothesis, oviduct tissue was incubated in vitro with or without testosterone. Estradiol levels in the medium were much higher when testosterone was present, indicating that aromatization can occur in the oviduct.