The case of a 7-month-old Nigerian child who presented with anemia and microcytosis is described. Hemoglobin electrophoresis studies revealed a band with pronounced cathodic mobility. This represented a heterohybrid hemoglobin tetramer composed of an α-globin mutant, G-Philadelphia (αGPhil), and two variant β-globin chains, βC and βO-Arab. The absolute amounts of αGPhil found in the propositus were less than expected for an α2-globin gene product. It has not been established whether αGPhiladelphia interacting with βO-Arab and βC globin chains is the cause of the microcytosis.