The Sp alpha I/65 variant of the spectrin has been recently described in black people with hereditary elliptocytosis (HE). The present study reports on a similar Sp alpha I/65 variant in nine North African persons belonging to four unrelated families. The abnormality was associated with a variable degree of elliptocytosis. In one case, red cell morphology was normal. In the nine carriers of the biochemical abnormality, the spectrin dimer self-association was defective. The association constant was reduced: 0.65 to 1.7 X 10(5) M-1 (controls: 4.6 +/- 0.5 X 10(5) mM-1 (n = 21)); in six cases, there was a higher level of spectrin dimer in the low ionic strength extract at 4 degrees C: 13.0 to 19.7% (controls: 6.4 +/- 2.1% (n = 7)). Limited tryptic digests of spectrin from the nine persons revealed a decrease of the 80,000-dalton alpha-1 domain, and the concomitant appearance of a peptide with a molecular weight of 65,000 daltons and an isoelectric point ranging from 5.0 to 5.1. There was a correlation between the proportion of the 65,000-dalton fragments, the defect of spectrin self-association, and the extent of morphological alteration. This is the first large series concerning a spectrin abnormality in non-black persons. In North Africa, cases of HE that are not due to a protein 4.1 defect have turned out so far to be associated with the Sp alpha I/65 variant.