17 chromosomally unbalanced patients, their siblings and parents were tested for HL-A types and for up to 25 other polymorphic systems to determine whether there was gain or loss of an allele concurrent with the gain or loss of chromosome material. 5 patients had trisomy of part or all of a chromosome; 2 had trisomy of a segment and also deletion of chromosome material. All 7 were due to a familial translocation. The remaining patients had small deletions; 5 had ring chromosomes, 4 had rod deletions and 1 had missing chromosome material due to a heritable translocation. All cases were informative at the HL-A loci because of the high degree of polymorphism of the system whereas only some of the other systems were informative. None of the 17 patients showed unusual inheritance of HL-A or any other of the polymorphic systems examined. These results provide evidence excluding the HL-A and other loci from a number of possible locations in the human genome.