Phosphoglycerate kinase (PGK) deficiency is generally associated with chronic hemolytic anemia, although it can be accompanied by either mental retardation or muscular disease. Genomic DNAs of two PGK- deficient patients previously described in France were sequenced directly after polymerase chain reaction amplification. The PGK Creteil variant arises from a G-->A nucleotide interchange at position 1022 in cDNA (exon 9), resulting in amino acid substitution 314 Asp-->Asn in the C-terminal domain, which contains the nucleotide binding site. It is associated with rhabdomyolysis crises but not with hemolysis or mental retardation. In the other case, which is associated with chronic hemolytic anemia and mental retardation (PGK Amiens), an A-->T nucleotide interchange was found at position 571 in cDNA (exon 5); this leads to amino acid substitution 163 Asp-->Val in the N-terminal domain, which contains the catalytic site for phosphoglycerate binding. These results corroborate the kinetic data observed. In the two cases, the mutations are distinct from others previously reported and no significant relationship could be observed between the location of the amino acid substitution and its clinical consequences.