1.

Penicillin (20,000 units in water) was given to twenty-two infants ranging in age from one week to 5 months and ranging in weight from 6 to 12 pounds.

2.

Serum levels were determined one-half, one, two, three, four, and six hours after ingestion of the penicillin.

3.

At one-half hour, the average of six measurements was 0.880 unit per cubic centimeter. At one hour the average of twenty-two measurements was 0.584 unit per cubic centimeter. At two hours the average of ten measurements was 0.360 unit per cubic centimeter. At three hours the average of twenty-two measurements was 0.265 unit per cubic centimeter. At four hours the average of five measurements was 0.045 unit per cubic centimeter. At six hours no penicillin was found in the serum of the five infants tested.

4.

All the levels up to and including three hours after ingestion were therapeutically adequate.

5.

Some of the factors which might be involved in producing high, sustained levels in young infants after oral administration of penicillin are discussed.