Meprins are membrane-bound oligomeric metalloendopeptidases belonging to the astacin protein family. The meprin isolated from human small intestinal mucosa was originally known as N-benzoyl-L-tyrosyl-p-aminobenzoic acid (PABA peptide) hydrolase (PPH). Here we describe the first genetic marker for the human MEP1A gene encoding the alpha subunit of this enzyme. The polymorphism changes codon 176 of the mature alpha chain of PPH from CAA to CAG. Using the polymerase chain reaction, this variation is easily detectable as a HhaI restriction fragment length polymorphism. The two alleles are both common, probably in all major races.