The present study investigated effects of chronic treatment with corticosterone (B) on larval development of the amphibian Xenopus laevis. Tadpoles (stage 51) were treated with B (100, 500 nmol/L), 50 mg/L of the anti-thyroidal substance ethylenethiourea (ETU), and a combination of ETU (50 mg/L) plus B (500 nmol/L) to address corticosteroid effects in the presence or absence of thyroid hormones (TH). ETU-treated tadpoles displayed developmental arrest, reduced levels of TH receptor beta (TRbeta) and prolactin (PRL) mRNAs, but increased expression of thyroid-stimulating hormone (TSHbeta). Tadpoles exposed to B were characterized by asynchrony of metamorphic tissue remodeling and decreased mRNA expression of corticotropin-releasing factor (CRF). Cotreatment of ETU and B reversed the effects of ETU on PRL and TSHbeta expression but did not alter ETU effects on development and TRbeta expression. Our findings confirm that chronic treatment with high doses of corticosteroids has teratogenic effects on developing tadpoles and additionally suggest a stimulatory effect of B on gene expression of the antimetamorphic pituitary hormone PRL.