In order to map the autosomal dwarf (adw) locus in the chicken, 11 segregating families were created. Initially five of these families were used for a linkage experiment in which the genome was scanned with microsatellites using a technique called bulked segregant analysis. Subsequently animals from 11 families were typed individually for microsatellites that appeared to be linked. We were able to detect genetic linkage of the adw locus to five different microsatellite markers on chromosome 1, the closest showing a recombination fraction of only 0.03 (LOD score 32.12). In mice the phenotype in chickens, both having a disproportionately large head. The pygmy locus has been mapped on mouse chromosome 10 and found to represent a mutation in the gene coding for high-mobility group protein I-C (HMGI-C). Considering the synteny between regions of chicken chromosome 1, mouse chromosome 10 and human chromosome 12, and taking into account both the phenotypic characteristics and the mode of inheritance of the chicken adw and the mouse pygmy loci, the HMGI-C gene is a major candidate gene for the adw locus in the chicken. Fluorescence in situ hybridization of metaphase chromosomes with the chicken HMGI-C gene as a probe, showed that the chicken HMGI-C gene is indeed closely linked to marker LEI146 on chromosome 1.