Several approaches have been used in this laboratory for the chromosomal localization of cloned human genes and for efforts to identify genes involved in genetic diseases and human neoplasia. The mapping approaches are complementary and include Southern analysis of DNAs from a panel of well-characterized human-rodent somatic cell hybrids, in situ hybridization of metaphase spreads with either 3H-labeled or biotinylated probes, and genetic linkage analysis in the 40 large C.E.P.H. kindreds as well as families with genetic diseases using restriction fragment length polymorphisms detected in the laboratory as markers. About 15-20 additional genes have been mapped by each method during the past year. The specific approaches have varied to provide information concerning gene size and organization, copy number, presence of alternative splicing, amplification of entire chromosomal regions, and other features. Our cytogenetic techniques have been improved to allow chromosomal localization of single copy genes by in situ hybridization with biotinylated cosmid probes and used to map the human thyroid peroxidase gene to chromosome 2p25.3 (telomere). Techniques have been developed to permit subsequent banding of the chromosomes after hybridization and propidium iodide staining thereby permitting chromosome identification and localization of the hybridizing sequence to a specific band. This represents a significant improvement in existing cytogenetic technology. Other highlights include the mapping of an expressed gene isolated by Drs. Klein & S. Donohue to the pseudoautosomal region of the X (and Y) chromosome and this represents only the third gene assigned to this region. An alphoid satellite probe from a clone isolated by Dr. H. Ozer has been found to identify human chromosomes 1, 5, and 19 and it may have a clinical human cytogenetic application. A linkage map of four probes spanning a 15cM region of chromosome 22q11.2 including a region involved in the DiGeorge Syndrome has been completed and additional genes have been added to a cluster previously mapped in the laboratory at 22q12.