We previously reported the isolation and characterization of cDNA clones encoding novel lipopolysaccharide (LPS)-inducible mRNAs from murine peritoneal macrophages. We now present the complete coding sequence of a cDNA previously termed D3. Analysis of multiple clones from a murine macrophage cDNA library provided a complete cDNA sequence of approximately 1.6 kb. The corresponding RNA contains a single open reading frame encoding a hydrophilic protein composed of 425 amino acids and is characterized by a region including three perfect and two imperfect repeats of a seven-amino-acid sequence. Based on nucleotide and deduced amino acid sequence, this mRNA is a new member of a previously described multigene cluster of interferon-inducible genes termed the Mouse 200 series genes. This new sequence most closely resembles gene 204 because both D3 and 204 genes have segments containing the seven-amino-acid repeat sequence. The Mouse 202 and 204 genes, however, have an approximately 200-amino-acid carboxyl-terminal domain that is absent in the LPS-inducible macrophage-derived cDNA. In addition, D3, 202, and 204 can all be distinguished from one another by virtue of unique 3' noncoding regions 200-300 base pairs in length. The D3 unique sequence is largely restricted to the smallest of the three size classes of this gene family expressed in macrophages and is not detected in interferon- or platelet-derived growth factor-stimulated fibroblasts. Overall, three separate mRNAs have now been described, each of which has three or more of a possible seven nucleotide sequence domains. Although the function(s) of the members of this gene family remains unknown, the multiple forms inducible by diverse stimuli and their restricted cell type expression suggest diverse and important physiologic roles for their products in inflammation.