Recombinant inbred (RI) strains are formed from an outcross between two well-characterized inbred stains followed by at least 20 generations of inbreeding. RI strains can be utilized for the analysis of many complex phenotypic traits. The LEXF/FXLE RI strain set consists of 34 RI strains derived by reciprocal crossing of LE/Stm and F344/Stm. Here, we report on genetic dissections of complex traits using this RI set and their parental strains. We have developed strain distribution patterns for 232 informative SSLP markers. The framework map covers the rat genome except for chromosome Y. Seventy-six phenotype parameters, which included physiological and behavioral traits, were examined for these recombinant inbred lines. The QTL analysis of these parameters revealed 27 significant and 91 suggestive quantitative trait loci, illustrating the potential of this RI resource for the detection of underlying gene functions for various phenotypes. Although this RI set was originally developed to study susceptibility toward chemical-induced tumors, it has been shown to be equally powerful for a wide spectrum of traits. The LEXF/FXLE RI strains have been deposited at the National Bio Resource Project for the Rat in Japan and are maintained under SPF conditions. They are available at http://www.anim.med.kyoto-u.ac.jp/nbr. Key words: Rattus norvegicus, recombinant inbred rats, QTL mapping, physiological traits, genetic.