Best's vitelliform macular degeneration has been genetically linked to chromosome 11. Subsequently, the disease locus has been refined to an interval between D11S903 and PYGM and, more recently, between D11S986 and D11S480. The gene encoding ROM1, a photoreceptor-specific membrane protein, has been independently mapped within the Best's disease region and has thus become a strong candidate for the Best's disease gene. In this study, we have mapped ROM1 relative to Best's disease and the loci D11S986, UGB (uteroglobin), and PYGM (human muscle glycogen phosphorylase) in recombinant Best's disease chromosomes. We demonstrate that UGB is localized proximal to ROM1 and that both UGB and ROM1 recombine with the disease phenotype. Thus, this analysis excluded ROM1 as the Best's disease gene.