The majority of the world's human population experiences a decline of lactase gene expression during maturation, so-called lactase nonpersistence. Thus, adults with lactase nonpersistence are susceptible to developing symptoms of lactose intolerance. By contrast, lactase persistence is an autosomal dominant heritable condition that results in a high level of lactase gene expression throughout adulthood and sustained lactose tolerance. Lactase persistence has recently been correlated with a single nucleotide genetic variant (a C --> T mutation) located 13,910 bases upstream from the lactase structural gene. We aimed to develop a restriction fragment length polymorphism (RFLP) method of detecting the C/T variants as a means of identifying individuals genetically inclined toward lactase persistence or nonpersistence. Genomic DNA in a 210-bp region surrounding the -13,910-bp variant site was PCR amplified with unique primers designed to avoid or mutate adjacent restriction sites. The amplified DNA was digested with a restriction enzyme, CviJI, that recognizes the base pair sequence generated by the lactase nonpersistence variant. Restriction digest gel analysis yielded DNA fragments of the expected diagnostic molecular weight sizes for individuals that were homozygote or heterozygote for the lactase persistence and nonpersistence variants. The genotypes predicted by the RFLP-based method were confirmed by DNA sequence analysis. The RFLP-based method provides a quick and noninvasive means of molecular detection of the presence or absence of the lactase persistence variant.