It was shown in previous work (Evans, 1958) that a cereal diet supplemented with 7% of white-fish meal supplied around 0·76% of lysine and 0·5% of methionine plus cystine. The addition of more pure l-lysine monochloride or dl -methionine to this animal-protein diet failed to bring about any significant improvement in the rate of growth, efficiency of food conversion or in the nitrogen retention of the pig, in the critical period between weaning and 80 lb. live weight. When the same cereal diet was supplemented by as much as 20% of ex. dec. ground-nut meal, however, the lysine content amounted to only 0·62% but the methionine plus cystine was 0·53%. On adding 0·2% l-lysine plus 0·2% dl-methionine to the 20% ground-nut diet the utilization of the nitrogen in the food was improved and the excretion of nitrogen in the urine was reduced. This finding was confirmed by means of a statistically designed growth trial, the daily rate of live-weight gain, improving from a mean value of 0·86 to 0·98 lb. following the addition of 0·2% of lysine and methionine, respectively, to the diet, the corresponding saving in meal consumption, between 35 and 80 lb. live weight, amounting to 16 lb. One group of ten pigs received a supplement of 0·2% of methionine only, and since it failed to show any improvement in performance over the control group it was concluded that 0·5% of methionine plus cystine must suffice to support satisfactory growth.