Mannose-binding protein (MBP, also known as Mannan-or Mannose-binding lectin) is a member of the collectin family of proteins (Turner 1996). Isolation and characterization of cDNAs from liver tissues of a number of mammals have provided important information about the primary structure of MBP. A single polypeptide chain of MBP is–30-32 kDa in size, but is assembled into a trimeric subunit. In human serum, several such subunits (three to six) are joined together, resulting in multimeric structures with M r of 250-370 kDa (Yokota et al. 1995). Rodents have two distinct forms of MBP (known as MBP-A and MBP-C), showing–55% identity at the amino acid level, suggesting that they are products of gene duplication (Drickamer et al. 1986). We previously described characterization of two forms of MBP cDNA from rhesus monkey liver library (Mogues et al. 1996). Unlike the rat insulin gene that appears to have duplicated in rodent lineage, but exists as a single copy in chicken and human genome, MBP gene appears to have undergone duplication prior to divergence of rodent lineage from other mammals (Perler et al. 1980). However, serological studies have indicated that, unlike old world monkeys, human and chimpanzee sera appear to have only one isoform of MBP, similar to rodent MBP-C (Mogues et al. 1996). To determine whether a homolog of rodent and rhesus MBP-A is expressed in human liver, we employed polymerase chain reaction technique, with primers corresponding to rhesus MBP-A cDNA sequences, to amplify the putative human MBP-A ortholog. We report here detection and characterization of a rhesus MBP-A-related transcript that is ex-