Quantitative trait locus (QTL) analysis is a statistical method for detecting precise location of chromosome regions associated with a particular phenotypic trait.In QTL detection,log odds (LOD) scores are calculated for marker loci as plausibility of the existence of QTLs (e.g.,Lander and Botstein,1989; Siegmund and Yakir,2007).However,the size of the maximum LOD score,its location,and the shape of the LOD score curve may be easily influenced by a few individuals and lead to unstable results.In this paper,we provide systematic methodologies for the detection of influential individuals that affect the LOD score curve.