An individual, whose parents are third cousins, has been shown to be homozygous for the rare Mi.V. condition. The proposita's red blood cells type as M−, N+(weak), S−, s+(strong), U+, Mi(a−), Vw−, Hil+; Wr(a− b−). The cells react, albeit less strongly than most other samples, with anti‐Ena. However, from studies on the red blood cells of the proposita and on those of another person of the En(a+), Wr(a−b−) phenotype, it is apparent that the term “anti‐Ena” actually describes a number of antibodies of differing specificities. Inhibition studies with sialoglycoprotein (SGP) isolates, and tests on protease‐modified red blood cells illustrate some of the differences in specificity.Biochemical analyses of the SGPs of the red blood cells of theMiVhomozygote and those of her parents confirm that the Mi.V condition is associated with the absence of normal MN SGP (α) and normal Ss SGP (δ), the appearance of a hybrid SGP molecule comprised of a portion of the MN SGP at its NH2 terminal end, and a portion of the S