Raw milk samples, collected from bulk milk tankers, are screened for the presence of tetracycline antibiotic residues. If tetracycline residues are detected, the milk will be shipped to an FDA laboratory for confirmation of the residues. Since the milk is shipped on ice blocks (4°C), it is important to know if and how long the residues are stable at this temperature. Control raw milk samples were fortified at 50 ppb with chlortetracycline, demeclocycline, methacycline, minocycline, oxytetracycline and tetracycline, aliquotted into polypropylene culture tubes, and stored at -70°C. Tubes were removed from the freezer and incubated at 4°C or 25°C, and were analyzed by the HPLC method of Carson J. AOAC Int. 76, 329-224 (1993)â. No loss of tetracycline residues in the milk was observed after 48 hrs storage at 4°C or 24 hrs at 25°C. Slight losses were noted after 72 hrs storage at 4°C and 48 hrs at 25°C under the conditions of the study.