This work describes the use of capillary zone electrophoresis for the characterisation of human milk proteins. The major proteins were identified following different strategies, such as the treatment with enzymes for selective protein modification. Using this method we studied the proteins in human milk from different donors throughout lactation. Qualitative and quantitative differences in the composition of the individual proteins were observed. The different beta-casein phosphoforms were separated and quantified. The average proportion of the 0P:1P:2P:3P:4P:5P was, approximately, 3:6:9:4:10:2. The evolution of the ratio of the different beta-casein phosphoforms during lactation is reported.