We describe the cloning and characterization of a rat single transmembrane protein that is homologous to the common neurotrophin receptor p75NTR in its death domain and the transmembrane region but dissimilar outside these regions. We have dubbed this protein PLAIDD, for p75-like apoptosis-inducing death domain protein. PLAIDD messenger RNA, which is ubiquitously distributed, is highly expressed in the embryo, but downregulated in adult tissues. Alternative splicing within the extracellular region of PLAIDD generates four RNA species, but only two of them are translated, PLAIDD_L and PLAIDD_S (long and short isoforms, respectively). While the amino acid sequence of the intracellular region of PLAIDD displays 41% identity with the intracellular region of p75NTR, the extracellular region of PLAIDD does not reveal any homology with p75NTR. Overexpression of each isoform of PLAIDD led to cytotoxicity in superior cervical ganglion neurons and in human embryonic kidney 293T cells. Both isoforms of PLAIDD could be co-immunoprecipitated with p75NTR, suggesting an interaction between these molecules.