Screening of single human chromosome plasmid libraries using a digoxygenin labelled (AAAT)15 oligonucleotide probe led to the identification of several positive clones. DNA sequence analysis of these was carried out and showed the presence of a number of simple DNA repeats. Oligonucleotide primers were designed from the sequences flanking these repeats and tested in PCR amplification reactions of human genomic DNA. Three of the markers tested were shown to be polymorphic with heterozygosities ranging from 40% to 69%. The markers were assigned to chromosomes using a panel of monochromosomal somatic cell hybrids combined with linkage analysis using DNA from the CEPH panel of families. The markers designated (AAAT)11, (AAAT)12 and (CA)19 were thus assigned to chromosomes 3, 21 and 20 respectively.