ApoA-I is the major apolipoprotein component of human high density lipoproteins (HDL). By a 2-D electrophoretic study of serum samples from Norwegian families, an apoA-I variant (apoA-I 2-1) was detected in a healthy individual. In the present study performed to elucidate formal and population genetic aspects of apoA-I, this variant was observed in 4 generations of the family of the propositus. One homozygous individual was found. A codominant autosomal Mendelian inheritance was established for the variant. Two heterozygotes were found among 124 unrelated individuals tested. The apoA-I 2 allele frequency was calculated as 0.008 in this population sample.