1. Experiments were undertaken to study the effect of daily intraperitoneal injection of acetoacetate for 90 days on vitamin B6 status in male albino rats. The initial dose of acetoacetate was 50 mg per kg body-weight, which was increased by 50 mg per kg body-weight every 15 days.

2. Urinary excretion of vitamin B6 was found to decrease after 30 days in acetoacetatetreated rats. After 75 days urinary values of vitamin B6 were considerably lower in such rats than in the corresponding control rats.

3. When acetoacetate injections were stopped after 90 days and the rats were fed L-tryptophan (100mg per rat), they were found to excrete significantly greater amounts of urinary kynurenine, hydroxykynurenine and xanthurenic acid than the corresponding controls.

4. Blood and liver vitamin Be levels were found to be lower in rats treated with acetoacetate for 90 days than in the untreated rats.

1. The fatty acid compositions of the plasma cholesteryl esters, phospholipids, triglycerides and unesterilied fatty acids were determined in two sheep at various times after they had been given intraruminal infusions of emulsions of maize oil or linoleic acid.

2. The concentration of linoleic acid in the plasma triglycerides began to increase 3 h after infusion began. The infusions of maize oil and linoleic acid resulted in the appearance of peak concentrations of linoleic acid in the plasma triglycerides 6 and 12h respectively after infusion began.

3. After the infusion of maize oil the plasma triglycerides showed an increasein theconcentration of stearic acid but after the infusion of linoleic acid the plasma triglycerides showed an increase in the concentration of oleic acid.

4. The concentration of linoleic acid in the plasma phospholipids and cholesteryl esters did not begin to increase until 6–9 h and 24–25 h respectively after the infusions had begun.

5. No evidence was found for an absorption mechanism which involved the direct incorporation of linoleic acid into the blood phospholipids or cholesteryl esters.

1. Four wether sheep were maintained on a diet of hay for 2 weeks and then starved for a period of 4 days.

2. Immediately before and during starvation the urinary excretion in the following fractions was determined: hippuric acid, creatinine, total diethyl ether-soluble acids of hydrolysed and unhydrolysed urine, total aromatic acids in hydrolysed and unhydrolysed urine and the proportion of the former present as benzoic and phenylacetic acids.

3. A method for determining the benzoic acid content of light petroleum extracts of urine has been developed and is described.

4. Starvation had little effect on the urinary excretion of phenylacetic acid or creatinine, but during the first 2 days of starvation there were large decreases in the excretion of all the other urinary fractions studied.

5. Of the fractions examined, 43% of the diethyl ether-soluble acids of hydrolysed urine and 42% of those of unhydrolysed urine were of exogenous origin; 76% of the total urinary aromatic acids were of exogenous origin. Partition of the aromatic acids in the urine of two of the four sheep indicated that the reduction in aromatic acid excretion on starvation was completely accounted for by the decline in benzoic acid output. Almost all the hippuric acid (97%) was of exogenous origin.

6. These results have been compared with the urinary output of aromatic acids by nonruminants when fasted, and possible reasons for the relatively large amounts of phenylacetic acid found in the urine of starved sheep have been discussed.