OBJECTIVE: To elucidate the molecular basis, hematological features, and electrophoretic and chromatographic mobility behavior of an unstable α METHODS: A Thai patient with unexplained chronic anemia and her daughter were investigated. Hematological data were analyzed using a standard automated cell counter. Hemoglobin was analyzed using high-performance liquid chromatography (HPLC) and capillary electrophoresis (CE). Mutational analysis was performed using appropriate polymerase chain reaction (PCR) techniques and direct sequencing. Additionally, α-globin haplotype analysis was conducted. Simple and rapid diagnostic methods were developed. RESULTS: Hemoglobin analysis in the patient revealed anomalous peaks separated from normal hemoglobin visible using the HPLC technique. These peaks were virtually absent in the daughter. DNA analysis identified a G to C mutation at codon 14 of the α CONCLUSIONS: Hemoglobin Jax, a pathological α-globin variant, is asymptomatic in simple heterozygotes and demonstrates more pronounced clinical effects when associated with deletional α-thalassemia. This knowledge can help develop strategies to prevent hemoglobinopathies in regions of high prevalence. Accurate identification requires DNA level analysis.