Hemoglobin Lufkin was found in a Black-American family. Structural analysis of the abnormal hemoglobin indicates a substitution of aspartic acid for glycine at position 29 in the beta chain. Marked instability of the variant hemoglobin is demonstrated by the rapid formation of inclusion bodies upon exposure of the red cells to redox dyes and by the large percentage of precipitated hemoglobin at 65 degrees C. The oxygen affinity, the Bohr effect, and the degree of cooperativity of Hb Lufkin and Hb A are similar over the physiologic pH range. However, at acid pH the oxygen affinity of the variant is increased. Unlike several other reported variants in the B helix, Hb Lufkin is not associated with methemoglobinemia.