We have discovered and characterized a compound polymorphic locus on chromosome 19, defined by an arbitrary genomic DNA segment cloned into a cosmid vector. Four different restriction fragment length polymorphisms with minor allele frequencies equal to or greater than 10% are revealed by Southern hybridization of subclones of cosmid 1-13 with TaqI, MspI, BamHI, and HindIII digests of human DNAs. Seventy-two percent of unrelated individuals are heterozygous at one or more loci, and seven of the 24 possible haplotypes occur with frequencies of 3%-38%. Using a somatic cell hybrid panel, we have mapped this locus to 19p13.2----19q13.3, whereas in situ hybridization suggests the probe is on 19p. Taken together, these results suggest localization to 19p13.2----19cen. The locus revealed by probes from cosmid 1-13 has been designated D19S11.