The present experiment was carried out to investigate the effect of fasting on the concentrations of plasma free amino acids in goats, and the following results were obtained.
1. The concentration of most of amino acids in the blood plasma tended to decrease with the lapse of day during fasting, though there was no significant difference. The concentration of total amino acids in the blood plasma decreased in response to the lapse of day during fasting.
2. Of the essential amino acids, methionine and tryptophane in the blood plasma rather tended to increase with the lapse of day during fasting. The pattern of essential amino acid obtained on the first day of fasting was little different from that obtained on the 6th and 7th days of fasting.
3. The ratios (glycine : valine or glycine : branched-chain amino acids) scarcely altered with the lapse of day during fasting. This suggestes that these ratios could not serve as useful index of nitrogen metabolism in goats when they are fasted.