Statistical analysis of data from calcium and hosphorus balance experiments with laying hens has shown that, for regression equations relating shell calcium to calcium retention:

(a) Individual birds give different regression coefficients (b values).

(b) The equations obtained for each of twelve birds belong to one family which can be represented by a more general equation.

(c) Over the whole of an experiment the b value and the phosphorus balance for each bird is significantly correlated with the total shell calcium secreted by that bird.

The metabolic significance of these findings is discussed in relation to shell formation and bone mobilization, and it is suggested that potentially high secretors of shell calcium are those which have a greater ability to lay down calcium on the bone during periods of low production and a greater ability to remove it from the bones when in high production.