AbstractMethodologies and tools for the construction of complete, primary genetic linkage maps of human chromosomes are emerging. Special families, optimal because of family structure for revealing linkage relationships, have been sampled and a number of genotypic determinations gathered. The associated genotypic database and the cell lines are available to the research community through theCentre d'Etude du Polymorphisme Humainin Paris, and form the basis for an international collaboration in the effort to map the entire human genome. Genetic diseases that are known only by their phenotype can be mapped to chromosomes when they co‐segregate with known map markers; localization of a disease gene represents an important step toward its characterization. New markers for hypervariable loci, highly efficient for mapping purposes, are being developed. Primary maps spanning several chromosomes are already in han