Genetic linkage maps are useful tools for defining the location of disease genes. Previously published maps of human chromosome 13 have been incomplete and have had ambiguities of order in the vicinity of the Wilson disease (WND) and retinoblastoma (RB1) genes. We have defined a six-locus map of this region using a large reference pedigree from Venezuela. Our map provides landmarks which will aid in the localization of WND, in determining the extent of deletions in retinoblastoma, and in the mapping of other marker loci.