Single-nucleotide polymorphisms (SNPs) are the subject of considerable attention for their potential as genetic markers. The National Institutes of Health (in particular the National Human Genome Research Institute and the National Cancer Institute) are devoting major funds to the discovery of SNPs and to providing resources to enable their use in gene finding and for other purposes. The Institutes are encouraging technical developments for SNP identification-aiming for as many 100,000. In addition, many genome-based companies are hunting for SNPs with the intention of patenting them. However, many questions remain unresolved; for example, what are the best strategies for finding SNPs, the number needed (present estimates have a ten-fold range from 30,000 to 300,000) and what commercial exploitation of SNPs might mean for their use. The objective of this workshop is to bring together a small group of scientists with backgrounds in population genetics, technology development and human genetics to discuss these issues. In addition, there will be participants interested in the broader policy issues raised by the debate over public and commercial availability of SNPs. We expect that the workshop will finish with participants drawing up a list of key problems that need immediate attention.