Measurement of serum enzyme activity is one of the most common laboratory tests. Increased activity may be caused by abnormal enzymes with a high molecular mass, the so-called macroenzymes. Macroenzymes may be seen in healthy subjects, but can also be related to disease. Macro-aspartate aminotransferase (macro-AST) is a macroenzyme that results from an enzymatic complex consisting of AST linked to serum immunoglobulin (IgA, IgG or both). MacroAST persistence is a rare benign condition. Macro-AST is generally characterized by increased serum AST activity. The article contains analysis of literature data on patients with macro-AST.