The data available so far on the microheterogeneity of human AFP are reviewed. Molecular and developmental bases for the microheterogeneity of human AFP are discussed. Special attention is paid to the application of the studies on AFP microheterogeneity for the prenatal diagnosis of developmental malformations and for the differential diagnosis of some cancers. The results obtained using different methods are compared with special reference to lectin affinity electrophoresis and lectin affinity chromatography. In addition, a self-explanatory nomenclature of AFP variants is proposed in order to simplify the comparison of results obtained by different investigators. This has already been accepted by several investigators. The eventual simplification of methods applicable for clinical purposes and especially the difficulties encountered in experiments with monoclonal antibodies are also discussed.