Selection for immune response parameters may lead to improved general diseaseresistance. Because disease resistance and immune response are hard-to-measurequantitative traits with low to moderate heritability, they may respond moreefficiently to marker-assisted selection (MAS) than to phenotypic selection. Todetect DNA markers linked to quantitative trait loci (QTL) associated withimmune response, a resource half-sib family of 160 backcross (BC1) andintercross (F2) birds was derived from a cross between two meat-type linesdivergently selected for high or low antibody (Ab) response to Escherichia coli.By using 25 microsatellite DNA markers covering approximately 25% of the chickengenome, initial genotyping of 40% of the resource family was followed bycomplete genotyping of the entire family with four suggestive markers. Three ofthese markers exhibited significant association with immune response: (1)ADL0146 on Chromosome 2 associated with Ab to SRBC and Newcastle disease virus(NDV), (2) ADL0290 on linkage group 31 affecting Ab to NDV, and (3) ADL0298 onlinkage group 34 associated with Ab to E. coli and survival. The family was alsogenotyped with five linked markers from two of the suggested regions, andinterval mapping was applied. The results confirmed the significant effects,suggested the location of the QTL, and confirmed the genetic association betweenimmune responses and disease resistance. These findings support the idea ofimproving poultry immunocompetence by MAS.