Isoelectric focusing can reveal at least two heterozygotes of the Amy1R class of variants. Family data on these variants show co-dominant inheritance for both alleles with respect to the normal Amy1A allele. The frequency of the alleles Amy1R1 and Amy1R2 in the Dutch population (n = 144) amounts to 0.006 and 0.03, respectively. Electrophoretic analysis of whole parotid saliva from different Amy1R phenotypes and of purified normal and Amy1R1 gene products indicates that the variant proteins differ from the normal protein by enhanced deamidation of asparagine and/or glutamine residues.