A galactose-binding lectin isolated from the venom of Trimeresurus stejnegeri is a homodimer C-type lectin. The cloned cDNA encoding the monomer of Trimeresurus stejnegeri lectin (TSL) was sequenced and found to contain a 5'-end non-coding region, a sequence which encodes 135 amino acids, including a typical 23 amino acid signal peptide followed by the mature protein sequence, a 3'-end non-coding region, a polyadenylation signal, and a poly(A) region. To completely characterize the deduced amino acid sequence, on-line HPLC-MS and tandem MS were used to analyse the intact monomer and its proteolytic peptides. A modified peptide fragment was also putatively identified by HPLC-MS analysis. The deduced amino acid sequence was found to contain a carbohydrate-recognition domain homologous with those of some known C-type animal lectins. Thus TSL belongs to group VII of the C-type animal lectins as classified by Drickamer [(1993) Prog. Nucleic Acid Res. Mol. Biol. 45, 207-232]. At present, a number of C-type lectins have been purified from snake venom, but most of them have been characterized only at the protein level. To our knowledge, this is the first known cDNA sequence of a true C-type lectin from snake venom.