In a previous report (Palyga, J., Biochem. Genet. 29, 431–445, 1991), three subtypes of erythrocyte histone H1 were found to vary in a Japanese quail population. While H1.b and H1.z histones were each represented by two electromorphs differing in apparent molecular weights, a polymorphism of histone H1.a was connected with a lack of this protein in some birds. As a genetic basis for this variability was demonstrated only in H1.b, here genetic data are provided which indicate that both H1.a and H1.z are encoded by two codominant alleles at a locus. A linkage analysis of family data in 13 quail pedigrees has revealed a significant linkage between H1.a and H1.z and between H1.b and H1.z (lod scores about 12 and 5, respectively). Thus, a gene for histone H1.z is located between H1.a and H1.b in the quail genome.