1. Eighteen crossbred wethers were allotted at random (six per treatment) to each of the following diets: (1) maize-silage; (2) grass-silage; and (3) chopped hay. After 6 months a single oral dose of D-α-[5-Me-3H]tocopherol was given to each sheep on these three treatments.
2. Blood plasma, rumen liquor and urine radioactivity were measured for 4 d and, at the end of this period, the animals were killed and tissue distribution of 3H was determined.
3. Maize-silage generally contained less α-tocopherol than grass-silage or hay. Tissue uptake of 3H was greater on maize-silage than other diets.
4. In muscle, spleen and liver, tocopherol concentrations were lower in the maize-silage than the grass-silage fed animals.
5. A tendency to higher uptake of radioactivity was recorded at all times in the plasma and its lipid extract of sheep fed on maize-silage than those fed on grass-silage or hay.
6. Urine clearance of radioactivity tended to be higher in animals fed on the maize-silage than those fed on grass-silage or hay. This difference of magnitude in urinary excretion was probably related to the rate of metabolism of the ingested radiotocopherol.