This RFA solicits applications for a cooperative agreement to augment the International HapMap Project by supporting the genotyping of approximately 2.25 million single nucleotide polymorphisms (SNPs) across the genome in 270 samples from four populations, at high quality and at a cost of about 1 cent per genotype. The data from this effort will contribute to the development of a map, called the HapMap, of the haplotype patterns in the human genome and of a set of SNPs that are informative about these patterns and the associations among the SNPs. The HapMap is expected to be a key resource that researchers will use to find genes that affect health, disease, and response to drugs and environmental factors. The genotyping supported by this RFA will augment the current efforts of the HapMap Project by substantially increasing the number of SNPs that will be studied, thereby increasing the quality of the HapMap and its usefulness as a resource for understanding human genetic variation and its role in health and disease. This RFA builds on a previous RFA, HG-02-005 Large-Scale Genotyping for the Haplotype Map of the Human Genome.