A rapid high-performance gel permeation chromatographic method to confirm the presence of enzymes with abnormally high relative molecular masses (macroenzymes) in serum is described. The technique requires 200 microliters of serum, can be automated and has been implemented for the analysis of creatine kinase (CK), lactate dehydrogenase, amylase, and alkaline phosphatase (ALP) activities. Serum fractionation according to relative molecular mass is completed within 21 min, and 84-106% of enzyme activities are recovered in the eluted fractions. The elution patterns obtained make possible the differentiation of 40 samples containing at least 10 U/l immunoglobulin-enzyme complexes, aggregated mitochondrial CK or membrane fragments carrying ALP activity from 40 control samples without these high-mass enzyme forms.