LOCI in the major histocompatibility complex (MHC) on chromo-some 6 and the insulin (INS) region on chromosome 11 have been implicated in susceptibility to insulin-dependent diabetes mellitus (IDDM) through candidate gene investigations^1–5, but they may account for less than 50% of genetic risk for the disease⁶. Genome-wide linkage studies have led to localization of more than 10 sus-ceptibility loci for insulin-dependent diabetes in the non-obese dia-betic (NOD) mouse7 and the BB rat⁸. Similar studies are now possible in humans through the development of dense genetic maps of highly informative microsatellite loci obtained using polymerase chain reaction analysis⁹. We have applied microsatellite markers from recent Genethon maps^10,11, and other highly informative mar-kers, in a genome-wide linkage study in IDDM. Here we report evidence for the localization of a previously undetected suscept-ibility locus for IDDM in the region of the FGF3 gene on chromo-some llq. Our result shows the potential of genome-wide linkage studies to detect susceptibility loci in IDDM and other multifactor-ial disorders.