A substitution of alanine for valine at position 126 in the beta-chain of hemoglobin was discovered in a hematologically normal adult male of Lebanese extraction. The variant beta-globin was initially observed and subsequently purified by reverse-phase high-performance liquid chromatography (HPLC). Reverse-phase HPLC was also used to isolate the variant tryptic peptide of beta-T13 that has alanine replacing valine at residue 126. The discovery of hemoglobin Beirut illustrates the usefulness of reverse-phase HPLC for the detection of neutral amino acid substitutions in proteins. The ability to detect neutral substitutions in undigested proteins is pertinent to the monitoring of genetic variation in human populations.