The proportion of unpigmented coat on the trunk was determined from photographsof 38 German Simmental and 627 German Holstein bulls distributed over threegenerations. All 665 animals were members of 18 Holstein and 3 Simmentalhalf-sib families. A Bayesian estimation of heritability yielded a posteriormean of 0.88 and a standard error of 0.08. A quantitative trait loci (QTL) scanover all chromosomes covered by 229 microsatellite marker loci (2926 cM) wasperformed by fitting a multiple marker regression model to 625 observations fromthe youngest generation in 18 families. On chromosome 6 a QTL for the proportionof white coat with large effects (experiment-wise error probability < .0001) wasfound and a less important one on chromosome 3 (chromosome-wise errorprobability < .009). Chromosome 6 is known to harbor the KIT locus (receptortyrosinase kinase), which is associated with various depigmentation phenotypesin mice, humans, and pigs. Similarity of phenotypic KIT effects in other speciesand synteny with the reported QTL suggest that KIT is a serious candidate genefor the degree of spotting in cattle. The results are also discussed withrespect to resistance to solar radiation, heat stress, and photosensitization.