Abstract: 1. After oral administration to rabbits and man, Funacillin was absorbed mainly in the small intestine and very slightly in the stomach and colon, reaching its peak concentration in the plasma in 4 hours, and then declining rapidly; a single dose (200 mg/kg body weight) given to a rabbit orally yielded in 4 hours a level of about 14 μg/ml and then a trace only at the end of 12 hours. 2.After absorption, Funacillin was distributed throughout different organs, as liver, brain (cortex, midbrain and brainstem), spleen, lung and kidney with varying degree of concentration which was highest in brain and spleen, the time of reaching its peak concentration in organs coincides with that in plasma. In the rabbits, whose liver function was damaged by carbon tetrachloride, the peak concentration in plasma was no higher than that in the normal rabbit. Ligation of the common bile duct caused a decrease in its concentration in plasma. 3. When incubated with slices of liver, brain, intestine and kidney, for 1 hour, Funacillin was not quantitatively recovered, because a certain amount had been decomposed by the tissue slices, particularly the liver. 4.Funacillin was excreted through the urine only in small amount (1—5% of the original dose). 5. Artificial pyrexia produced by subcutaneous injection of E. Coli vaccine to cats, was not abolished by Funacillin. 6. No demonstrable effect was observed on the blood pressure and respiration, when Funacillin was given intravenously to rabbits. 7. Funacillin did not prolong the anesthetic time of Evipan.