We report here the results of the analysis of aromatase and steroidogenic factor 1 (Sf1) expression in adult lung of the urodele amphibian Pleurodeles waltl. Using RT-PCR experiments, we show the expression of the estrogen-synthesizing enzyme, aromatase, in this organ. In the lung, no significant difference between males and females was observed in the level of aromatase mRNAs. Aromatase mRNA levels were also identical to those found in the brain or the testis, but the levels were 2-fold lower than in the ovary. Aromatase activity measurements revealed the presence of an active form of aromatase in the lung, which was similar in males and females. There was no difference in the level of aromatase activity between lung, brain, and testis, but a higher activity was measured in the ovary (13.7-fold compared with testis). Therefore, the differences in aromatase mRNA level between the ovary and the other organs did not mirror the differences in aromatase activity, suggesting the involvement of posttranslational events. Aromatase was also expressed in the lung of the anuran amphibian Xenopus laevis. In Pleurodeles lung, Sf1 mRNAs were also detected. There was no difference between males and females in the level of these mRNAs. The Sf1 mRNA levels were not significantly different from those measured in the brain, but a significant 2.1-fold higher level of expression was found in the gonads. These results demonstrate clearly the expression of steroidogenic markers in the adult lung of amphibians, but the biological significance of this remains to be determined.