As a very brief background, this database of hemoglobinopathy genotypes and phenotypes (called GenPhen) is designed to record information about individual patients. It will help establish what the range of phenotypes is for the various genotypes, and will provide useful information both to aid in diagnosis and in designing and prescribing treatments. We anticipate that it will facilitate identification of particular phenotypic features with certain ethnic groups or other subgroups. These latter observations should provide candidate patients to participate in studies designed to identify "epistatic modifier" genes, i.e. genes whose products affect the phenotype. A hypothetical example would be a gene encoding a regulatory protein that increased gamma-globin production in sickle cell disease.