We have previously described the structural identification of the sickle hemoglobin variant Hb C Ziguinchor (α2Aβ2 6 Glu→Val, 58 Pro→Arg). This hemoglobin was found in two generations (three members) of an African family. In two family members, the clinical picture resembled that typical of A sickle cell trait, while the third member showed a more extreme clinical condition due to complication by an iron deficiency anemia. The functional properties of llb C Zig. in red blood cells or in dilute solutions were identical to those of tib S. The gelling behaviour of deoxy Hb C Zig. was also indistinquishable from that of Hb S. These findings suggest that, in contrast to the cast of Ilb C Ilarlem, the second substitution in position P58 in tlb C Zig. does not interfere with the intrrmolecular interactions determined by the sickle substitution.