Protein disulphide isomerases belong to the thioredoxin superfamily of protein-thiol oxidoreductases that have two double-cysteine redox-active sites and take part in protein folding in the endoplasmic reticulum (ER). We report here the cloning of a Pichia pastoris genomic DNA fragment (2919 bp) that encodes the full length of a protein disulphide isomerase (PpPDI). The deduced amino acid sequence of PDI consists of 517 residues and carries the two characteristic PDI-type redox-active domains -CGHC-, separated by 338 residues, and two potential N-glycosylation sites. The N-terminal end forms a putative signal sequence, and an acidic C-terminal region represents a possible calcium-binding domain. Together with the -HDEL ER retrieval sequence at the C-terminus, these features indicate that the gene encodes a redox-active ER-resident protein disulphide isomerase. The nucleotide sequence, which also contains two other open reading frames, has been submitted to the EMBL Nucleotide Sequence Database, Accession No. AJ302014.