Abstract: A process for rapidly detecting as little as 0.001 I.U. ml of antibiotic in a sample of liquid such as milk. The process comprises the steps of incubating the sample together with a tagged antibiotic or antibiotic precursor and antibiotic sensitive cells under conditions which allow antibiotic molecules to attach to receptor sites in or on the cells, separating the cells with immobilized antibiotic from the remainder of the reaction mixture, and determining the quantity of tagged antibiotic on the cells. The amount of tagged antibiotic on the cells is a function of the quantity of antibiotic present in the sample. The process is well suited for detecting penicillin-type antibiotics and may be practiced using peroxidase-tagged 6-amino penicillanic acid and sonicated, penicillin supersensitive Bacillus stearothermophilus immobilized on a support.

Abstract: A process for rapidly detecting as little as 0.001 I.U./ml of antibiotic in a sample of liquid such as milk. The process comprises the steps of incubating the sample together with a tagged antibiotic or antibiotic precursor and antibiotic sensitive cells under conditions which allow antibiotic molecules to attach to receptor sites in or on the cells, separating the cells with immobilized antibiotic from the remainder of the reaction mixture, and determining the quantity of tagged antibiotic on the cells. The amount of tagged antibiotic on the cells is a function of the quantity of antibiotic present in the sample.

Abstract: A method of removal of penicillin from penicillin-contaminated milk, which method comprises contacting the contaminated milk with activated charcoal and recovering a penicillin-free milk product.

Abstract: A radioassay system for the determination of methotrexate in biological fluids based on the competitive binding of labeled and unlabeled methotrexate to the enzyme dihydrofolate reductase. Samples of unknown methotrexate level are mixed with I.sup.125 labeled methotrexate. A portion of the total methotrexate present is bound by the addition of enzyme, and the unbound methotrexate is removed with charcoal. The level of bound I.sup.125 labeled methotrexate is measured in a gamma counter. To calculate the methotrexate level of the unknown samples, the displacement of bound labeled methotrexate caused by the unknowns is compared to the displacement caused by known methotrexate standards.

Abstract: A radioassay system for the determination of methotrexate in biological fluids based on the competitive binding of labeled and unlabeled methotrexate to the enzyme dihydrofolate reductase. Samples of unknown methotrexate level are mixed with I.sup.125 labeled methotrexate. A portion of the total methotrexate present is bound by the addition of enzyme, and the unbound methotrexate is removed with charcoal. The level of bound I.sup.125 labeled methotrexate is measured in a gamma ray counter. To calculate the methotrexate level of the unknown samples, the displacement of bound labeled methotrexate caused by the unknowns is compared to the displacement caused by known methotrexate standards.