Sequential Giemsa-11 and C-band staining of the heterochromatic region of chromosome 1 from 30 unrelated individuals revealed a high degree of variability within this region, more than was identifiable with either stain alone. The Giemsa-11 stained material usually appeared as a single band of only slightly varying size within the heterochromatic region. The position of this band ranged from a location immediately adjacent to the centromere, to one farther along the long arm or at the junction of the C-band heterochromatin and euchromatin. Two individuals had a chromosome 1 with no detectable Giemsa-11 band but an average-size C-band. Two others with a large heterochromatic segment by C-banding had two Giemsa-11 positive bands. Additional studies of five members of one family were consistent with transmission of these hetermorphisms in codominant Mendelian fashion.