Screening of a cDNA library from Porphyra yezoensis with probe based upon known glyceradehyde-3-phosphate dehydrogenase (GAPDH) genes identified a full-length clone apparently encoding chloroplast glyceradehyde-3-phosphate dehydrogenase ( GapA). Clone GAP4 contains the complete chloroplast-GAPDH cDNA of P. yezoensis, corresponding to a 72 amino-acid transit peptide and a 338 amino-acid mature protein. Multiple alignment of the predicted mature chloroplast-GAPDH subunit at amino-acid level clearly shows that four highly conserved regions in GAPDH are present in our cDNA clone. The GC contents of the entire region of the GapA cDNA (64.2%) were similar to the average GC content (65.2% ) which was obtained by Porphyra EST analysis. The position of red algae in phylogenetic trees inferred from GAPDH sequences was discussed. Sequences of chloroplast- GAPDH cDNA have been deposited in GenBank under accession number AY273819.