I945 SUMMARY-1. The retention of Ca by rats-receiving diets mainly consisting of wholemeal bread or of bread made from 72% extraction flour has been studied in metabolic experiments.2. In one experiment Creta praeparata or bone meal were added to the 72% extraction flour to. bring the Ca content of the diet to that of the wholemeal bread diet. In another, the two substances were added to the 72 % extraction flour at a rate equivalent to i lb. of CaCOJ/280 lb. sack of flour, and the wholemeal flour was similarly supplemented to bring its Ca content to the same level.3. In both instances Ca was less well retained from the wholemeal bread diets than from the diets containing bread made from lower extraction flour, and the evidence strongly suggests that this was due to the depressing effect ofthe phytic acid present in wholemeal bread. These results confirm the obser. vations on man by McCance & Widdowson (1942a).4. The wholenxeal bread diets -promoted better growth in rats than the 72 % bread diets.We are greatly indebted to Dr P. Halton