Using a subtractive cDNA cloning method, we isolated a number of T-lymphocyte-specific genes. One of these genes, represented by the cDNA clone pT49, is expressed in cytotoxic T lymphocytes but not in helper T lymphocytes or B lymphocytes. The protein structure deduced from the nucleotide sequence showed a high degree of homology to fibrinogen beta and gamma subunits. This might indicate that evolutionarily fibrinogen has its origin in lymphocytes. In spite of the strong homology of pT49 protein to the fibrinogen subunits, the positions of the introns in the pT49 gene are totally different from those of the fibrinogen genes.