The most common kappa casein (kappa-CN) variants, kappa-CN A and kappa-CN B, are synthesised differentially in the lactating mammary gland of heterozygous animals (kappa-CN AB). In this study we evaluated several approaches for quantification of allele specific mRNA transcripts. The most consistent results were obtained using allele specific RT-PCR and capillary electrophoresis. On average, 13.4% more allele B specific than A specific transcripts were found. DNA sequencing of the proximal promoter region in several homozygous animals (kappa-CN AA, BB, EE) did not reveal any allele specific polymorphisms. Using the EMSA and DNase I footprinting we confirmed functional binding sites for three transcription factors (AP-2, NF1 and MGF) within the kappa-CN proximal promoter region. Sequence analysis of the 3'-UTR of the kappa-CN gene revealed seven allele specific sites. Two of these allelic differences were close to previously identified 3'-end regulatory sequences. In addition, allele specific differences in length between mRNAs of both variants were found. The two later findings suggest a possible post translational control determining content differences of kappa-CN in milk.