The netrin family of proteins, found throughout the animal kingdom, are well known for their roles in developmental signaling. Netrin-1, the best-studied member of this family, signals through four receptor types in vertebrates: the UNC-5 family, DCC, neogenin, and DSCAM. We have previously characterized a netrin-1-like protein in the ciliated protozoan, Tetrahymena thermophila. This protein is secreted from Tetrahymena, and functions as a chemorepellent. Since a netrin-like protein is produced by this organism, we hypothesized that some components of the vertebrate netrin signaling pathway might also be present in Tetrahymena. Through immunolocalization on the plasma membrane of the cell, we have found that Tetrahymena appear to have a UNC-5 like protein, as well as proteins that are immunologically similar to neogenin. A homolog of src-1, a tyrosine kinase involved in vertebrate netrin-1, is also present in Tetrahymena. Future experiments will allow us to make more comparisons between netrin signaling in Tetrahymena with netrin signaling in the animal kingdom, and will allow us to determine the suitability of Tetrahymena as a model system for this particular pathway.