Lactate dehydrogenase (LDH) was purified and crystallised from the liver of immature (4 weeks), young (22 weeks) and old (116 weeks) female rats and the kinetic, physical and chemical properties of the purified enzyme were studied. Even though slight differences existed in effect of pH, temperature, storage and ratio of A280/260, significant differences were not observed in kinetic properties, behaviour on polyacrylamide gels, ion-exchange chromatography column, and -SH groups among the three age groups. These data indicate that, unlike muscle LDH of old rats which had shown altered properties (earlier report from our laboratory), liver LDH is an unaltered, like LDH of heart. The possible reason for the unaltered nature of the liver LDH may be: (a) the tissue origin; (b) the gene responsible for its synthesis is expressing well even in old age; or (c) non-influence of post-translational modifications on the enzyme molecule.