Cereal genotypes exhibiting a dwarfed phenotype played an important role during the 'green revolution' between 1960 and 1970, when the exploitation of dwarfing mutants allowed for the development of high yielding cultivars with an improved harvest index. In a number of cases the functional basis of dwarfing phenotypes is due to a mutation in a gene of the gibberellic-acid (GA) biosynthesis pathway (GA-sensitive mutant) or of the GA signal transduction (GA-insensitive mutant). The emphasis of the present work was to develop a high resolution map and to achieve marker saturation of the gai region, as a precondition for the map-based cloning of this gene. Based on observations from previous studies regarding conservation of marker orders and orthologous relationships between GA-insensitive genes across grass genomes generally and between the genomes of barley and rice in particular, a synteny-based strategy was chosen. Comparing the barley and rice genetic linkage maps, it was possible to identify theoretically a syntenic region of rice chromosome 7L and finally, to confirm this synteny by integrating seven rice markers into the barley genetic map. Based on the observed colinearity between both genetic regions a corresponding rice contig was identified in the available YAC and BAC / PAC maps. The analysis of the defined YAC contig led to the detection of three new YAC originated rice markers for the gai region. Out of these, two markers could define the final target interval (0,55 cM) in barley, and by electronic chromosome walking the physical target region (~ 224 kb) consisting of four rice BAC clones. Three putative open reading frames (SORF I - III) were identified in the rice sequence data (RiceGAAS) exhibiting significant sequence similarity to known signal transduction genes. By using sequence homologous wheat and barley ESTs, two of these rice-ORFs (SORF I and III) could be mapped in barley, flanking the gai Locus directly. Based on its physical position between SORF I and III, the third rice-ORF (SORF II) could be the supposed gai candidate and might serve as a starting point for the map-based isolation of the gene in barley. The present, comparative and high resolution study between barley and rice in the gai region revealed a stable orthologous relationship, based on the integration of 10 rice EST markers of the genetic and two putative rice genes ('SHR-like' und 'GA-regulated') of the physical rice target region.