Combined linkage and linkage disequilibrium analysis were used to refine theposition of a previously detected QTL affecting milk production traits on bovinechromosome 6. Through a series of single- and multitrait and single- andmultipoint QTL analyses, the QTL could be positioned to a 7.5-cM intervalsurrounded by the markers BMS2508 and FBN12. The most significant results werefound for fat percentage and protein percentage. This effect seemed to be causedby a QTL allele embedded in one specific marker haplotype that caused areduction in fat and protein yields and a concomitant increase of milk yield,thus resulting in a marked reduction of fat and protein percentages.