Summary The results are in general agreement with those of our previous work. The rachitic nature of the changes produced by feeding a 20 per cent. yeast diet has been confirmed. Rickets was prevented by addition to the yeast diet of either cod liver oil or calciferol (1190 i.u. of vitamin D per day) and was rapidly cured by larger doses of calciferol: it was almost completely prevented by addition of 4 per cent. of calcium carbonate. When 6 per cent. sodium phosphate (Na2HPO412H2O) was added to a normal diet containing meat and bone meal, rickets failed to develop, but three of six pigs died after two to three weeks with gastro-enteritis. The survivors showed no evidence of rickets and it thus appears that the rachitogenic effect of yeast is not due merely to its high content of available phosphorus. The exact mechanism of the production of rickets in pigs on a high yeast diet remains unknown.