GLIAL cell-line derived neurotrophic factor (GDNF) and neurturin (NTN) are members of a new family of factors within the transforming growth factor-βb(TGFβ) super-family. Signaling by GDNF and NTN depends on the tyrosine kinase receptor Ret and on GFRα−1 and −2. We have investigated by competitive RT-PCR the developmental expression of these molecules within the rat hippocampus. All transcripts reach high expression levels between postnatal day 0 and 14 (P0–P14), a critical period of hippocampal differentiation, suggesting roles for these molecules in this process. All mRNAs (with the exception of Ret) can be detected as early as embryonic day 14 E14. The absence of Ret expression at E14 suggests that both GDNF and NTN may employ an additional, unknown receptor. NTN expression shows a biphasic expression pattern, with maximum expression levels at E14 and P5.