We report the cloning and characterization of a cDNA that encodes a functional human galactose-1-phosphate uridyl transferase (GALT). The cDNA is 1400 bases in length and encodes a 43,000 Mr protein. The cloning strategy involved the identification of short peptide sequences conserved between the homologous enzymes from Escherichia coli and yeast, and the construction of oligonucleotide pools corresponding to the conserved patches. These patches of conserved amino acids tend to be conserved in humans as well.