An autosomal genome scan for quantitative trait loci (QTL) affecting milkproduction traits was carried out on the Norwegian Dairy Cattle population. Sixhalf-sibling families with a total of 285 sons organized according to agranddaughter design were analyzed by a multiple marker regression method.Suggestive QTL for one or several of the five milk traits (milk yield, proteinpercentage, protein yield, fat percentage and fat yield) were detected onchromosomes 3, 5, 6, 11, 13, 18 and 20. Among these results, the findings onchromosomes 3, 6, and 20 are highly supported by literature. The most convincingresult was found close to marker FBN9 on chromosome 6, where a QTL was detectedwith alleles that cause a marked reduction in both protein and fat percentagesand an increase in milk yield. The results for fat and protein percentage werehighly significant even after accounting for multiple testing across the genome.Using bootstrapping, a 95% confidence interval for the position of the QTL forthe percentage traits on chromosome 6 was estimated to 16 cM.