Methods currently recommended by French, European and International Societies for determining the catalytic concentration of Alanine Aminotransferase (ALT) are reported. These methods are very close, recommend the apoenzyme reactivation by pyridoxal phosphate and allow the transferability of the results from site to site. Complementary information concerning commercial kits, adaptation to enzyme analyzers, specimen collection and storage, reference values and biological variations in healthy subjects are also given. The adoption of these homogeneous methods should make easier the choice of a cutoff value for ALT among blood donors for the prevention of posttransfusion hepatitis.