We report the cDNA sequence of 3CH134, an immediate early gene whose transcription is rapidly and transiently stimulated by serum growth factors. 3CH134 encodes a 367 amino acid protein that does not share significant sequence similarity with any known protein. 3CH134 is inducible through multiple signal transduction pathways, and in the adult mouse is expressed predominantly in the lung. Using affinity-purified antibodies, we have identified the 3CH134 protein in serum-stimulated Balb/c 3T3 cells and determined that it has a short half-life.