Milk protein abundance was then analysed quantitatively using a Kodak imaging system (Fig. 3d and e) . In heterozygous mice the amount of a-casein protein is reduced by around 50% when compared to albumin (Fig. 3e) . In contrast, the relative amounts of b-casein and c-casein compared to albumin remain constant. In the milk derived from homozygous a-casein deficient mice, no acasein protein can be detected (Fig. 2a, 3a and 3d ). In addition, the amounts of band c-casein are also significantly reduced (Fig. 2a,  3d and e) . Whereas the ratio of b-casein to albumin in control milk is 2:1, the ratio in milk from homozygous a-casein deficient mice is 1:1 indicating at least a 50% reduction in b-casein protein concentration in milk (Fig. 3d and e) . This reduction is also detected by Western blot analysis (Fig. 3b ) Analysis of the data using one-way ANOVA demonstrated that the changes in the concentration of band c-casein in the milk of a-casein deficient mice are highly significant (p.0.001; Table 5 ). The concentration of milk proteins (Fig. 3d) is consistent with published data [5] .