In four cases of human acrocentric ring chromosomes r(21)(p13q22); r(21)(p11q22); r(13)(p11q?); and R(21)(P11Q22), association of the annular with normal D and G chromosomes was found. This finding indicates that: 1) the "satellite" association is not terminal 2) the heterochromatic region (band p11) adjacent to the acrocentric short arm constriction contains nucleolar organizers (NOs), although bands p12 and 13 could not be excluded; and 3) band p11 probably has two different functional sites, a distal NO+ and a proximal NO-. Related studies on three C/G translocation carriers suggest a non-specific interphase interchromosomal relationship.