Genetic maps and populations are the basic tool with which nucleotide sequence and phenotypic traits are linked; they are important tools for gene and QTL mapping, and for functional genomics research. One of the most studied and phenotypically characterized rice gene-mapping populations available today is a set of 280 ‘Lemont'/‘TeQing' recombinant inbred lines (RILs) which has been used by various groups to molecularly map more than 200 agronomically important loci. To further evaluate the utility of the mapped foreign TeQing genes within a U.S. tropical japonica rice breeding program, a set of 250 backcross introgression lines containing portions of the TeQing genome now introgressed into a predominantly Lemont genetic background was subsequently developed at IRRI. A combination of RFLP markers and phenotypic characterization were used to follow targeted molecularly-marked genomic segments as they were introgressed into a predominantly Lemont background. The goal was to introgress all TeQing genes into one or more of the progeny lines, hereafter called TILs for TeQing-into-Lemont introgression lines. This population of 250 TILs was recently analyzed using 120 polymorphic SSR markers to represent all 12 rice chromosomes. Most of the TILs were found to contain multiple introgressions, more than just the one molecularly-targeted introgression per TIL. This benefits genetic research by providing more replication and fixed recombination than anticipated of each TeQing chromosomal segment within in the TIL population. Molecular characterization of the introgressed regions in the TILs allows us to conduct detailed comparative genomic analysis of rice genes. This population of TILs has already been used to verify the location and phenotypic effect of several QTL for sheath blight resistance and mesocotyl elongation that were first putatively mapped using the related Lemont/TeQing RIL population. The TILs were also used for denovo mapping of a QTL causing spreading culms, a plant architectural trait.