cDNA fragments of ovine liver pyridoxal kinase were amplified by PCR using degenerate oligonucleotide primers derived from partial amino acids sequences of the enzyme. Using PCR products as probes, several overlapping cDNA clones were isolated independently from an ovine liver and a human brain cDNA library. The largest cDNA clone for each was selected for sequence analysis. The ovine liver cDNA encodes a polypeptide of 297 amino acid residues with Mr of 32,925, whereas the human clone is comprised of an open reading frame encoding 312 amino acid residues with Mr of 35,102. The deduced sequence of the human brain enzyme is completely identical to that of human testes cDNA recently reported (Hanna et al., 1997). The ovine enzymes have approximately 77% sequence identity with the human enzyme although the two sequences are completely different in the N-terminus comprising 32 residues. This result suggests that pyridoxal kinase is highly homologous in mammalian species.